Hub is C8 Pro running 2.4.4.151 platform and using ZWaveJS.
OBSERVATION: With every other platform update ZWave performance gradually degrates. Please don't ask me for any logs, etc. The simple answer is: random delays are getting longer and entirely mising commands happens more often. The system is pretty much the same for a long time. Yes, ocasionally some RM Rules are modified and basically no new devices are added. The biggest variavble is: new updated platform (and whatever custom drivers are getting latest updates but these is seldom cases). And I did updated the ZWave Radio in that very nerrow window when update was introduced and almost immidietly was removed.
THE QUESTION IS: Is any tweaks could be done in order to improve ZWave performance except for the (endles) waithing for the potential platform improvements in the ZWave area?
I am looking for constuctive solid suggestions and not for something like to reboot hub every day (or so), etc.
Lots of discussion here on that.
Personally, I have no issues but my mesh is solid.
Search for Ghosts/removal as this is always the main issue. Have a look and provide your mesh device topology map and routes under Settings | Z-Wave details. The routes should all be populated.
Then pretty hard for folks to provide any help targeted at whatever specific issues you may be experiencing.
Rebooting your hub on a schedule can be a constructive/solid suggestion that some members use/rely on. Especially if you don't want to spend time digging into specifics of your hub, if a scheduled reboot resolves your performance issues (you didn't say if it does or doesn't) then why not just set up a scheduled reboot? 
I've been on JS for quite a while now an don't run into your issues w/degrading performance over time, but I've spent time looking at my general logs, and Device & Application logs for potential signs of issues/problems and made changes (simplify or even remove a rule, swap out devices, etc.) to try to avoid problems.
The fact that your system has had the same issue for an extended period of time across multiple (many?) releases seems to indicate that your issues aren't related to any particlur platform version, but more a fundamental issue w/your combination/use of devices, your particular home's characteristics (size, layout, building materials), device types, and positioning of devices & repeaters that affect mesh devices.
I have seen some folks who have issues on JS w/some specific devices who switch back to ZipGateway and are fine there...that might be an option you could investigate.
There is no gosts. I did not add/modify anything in the ZWave area for years. The only diffrense is - platform updates resulting in general gradual hub performonce degradation. The ZWave Mesh happems to be the most sensitive area (maybe because switching to ZWaveJS as well).
BTW, when I switch to ZWaveJS there are few battery powered devices with no routes but they are working just fine.
Do you mean this happens in your system every other release, or every release?
I have not observed this with about 40 z-wave devices in my mesh.
I mentioned this thousands times - there is no specific device in question. ALL the devoces exhibits a random delays. I cannot provide an endless logs for basically all devices. It is what it this - GENERAL RANDOM DELAYS, and now more and more completely missing commands.
THIS IS NOTHING MORE THAN MASKING TAPE FOR THE REAL PROBLEM!
(I am EE with huge experience, beleive me I know what is a FIX and what is a BANDAID.)
Yes, my system is very unique and very complicated. So what? There was no major changes for years. But yes, I am clearly seeing a performance degradation basically with every other platform release. This is pretty much clasic "one variable at a time" degugging approach.
I did switch between these two few times. And yes, at least in my case ZIP performance is much better (near ideal). But ZIP is EOL. And that is why I am waiting for the ZWaveJS to become rock solid solution for the ZWave Mesh.
I mean, I am seeing gradual performance degradation with near every new platform release. My total number od devices is 507. About half are ZWave toys. But general system configuration is about the same for years.
So you have ~250 z-wave devices? Spread over how many hubs?
All ZWave and all Zigbee devices are handled directly by C8 Pro. I have a C7 mainly handling few LAN Devices and HA for BT Devices and whatever HE is not capable.
Well that could be an issue. I don't know what the current recommendations are, but Hubitat used to recommend no more than ~100 z-wave devices on a single hub.
By way of comparison, I have had no z-wave or zigbee issues; I have ~40 z-wave devices and 135 zigbee devices on a single C-8 Pro.
~250 z-wave devices comes very close to the max number that can theoretically be part of a single mesh.
I had not seen that recomendation for no more than 100 ZWave devices. But say if I use more than one ZWave Mesh it could be even worse. The ZWave is using single frequency. More than one ZWave Mesh in the same band may create a lot of RF interference. Specifically because these multiple meshes will not have any arbitration in place.
Yes, single mesh is sort of limited to the 256 devices. However LR devices are outside this range. LR numbering starts with 0x1xx And BTW, the ZWave ID is 16-bits:
Yeah, I'm no help, you're in the big leagues. 
I have 52 ZW and 55 ZB and all is well.
Not really. It really doesn't care about other meshes, it cares about the controller. It's not a problem to have multiple z-wave meshes. Zigbee is a bit different in that respect.
Not really, unless the device density is very high. But in general, there is no issue because:
- Transmissions are very quick.
- Each mesh has a unique Home ID.
Than I a missing something. Multiple transmitters are firing on the same frequency with no arbitration and do not interfear? Or the ZWave protocol/controller has a buit-in collision detection and prevention mechanizm (similar to Ethernet or so)? But even if yes, there is a collision detection than I can clearly see a performance degradation because the ZWave speed is 100kbs max unlike enev very old Etherner nad 10mbs.
Well, no so quick - only 100kbs max.
Yes, but this will not prevent an RF Interference on the same frequency.
see @aaiyar 's comment
Zigbee is even faster - 250kbs and also has a unique mesh ID. But it also could yous a different RF Channels. Tell me plase why you don't want two or more Zibbee meshes on the same channel?
We're using "quick" in two different contexts. I am referring to the length of each transmission. Not the data transfer rate.
In general, Google searches seem to support the idea of keeping each z-wave mesh to around 100-120 devices. The same searches also do not indicate extensive contention between meshes.
In my opinion, because z-wave uses a "listen, then talk" approach to radio transmission, having around ~232 devices in a single mesh is more likely to cause random delays over having two meshes each with about 120 devices.
I run two Zwave meshes with no issue. One has 50 devices the other only 10. I guess because, as @aaiyar mention, the density is not very high.
