There are a lot of possible causes for many of the issues you describe, so it's hard to say where to start. I'm sure others will chime in too, but here are some ideas to start. (And: welcome to Hubitat, and sorry to hear you're having problems! Many of us came from ST, too, so you're at least in good company there.)
For the lock: that Schlage model (at least the non-Plus one) is notoriously problematic for some people. Firmware version seems to influence luck here, but I don't believe the firmware is upgradeable on the old ones. Having a strong Z-Wave network, including beaming-capable repeaters (preferably near both the hub and the lock) can be helpful. Some people have found that dedicated "repeater" devices like the Aeon or Ring are particularly helpful, perhaps because you have more control over their location (or they have better placed antennas and aren't shoved inside a wall like many repeaters), though they shouldn't theoretically be necessary.
Related to the issue you mentioned involving the lock, the mobile app's geofencing is unfortunately unreliable for some. Many people combine multiple options into one (or just use another solution entirely) in order to make this more reliable, which is a separate issue with several threads here you can probably find with ideas (or I can try to find some of them, too).
So, the lock issue could really be caused by geofencing events not being generated when they should be or the lock not responding to commands the hub sends. Device event history may help you narrow this down: under "Devices," find your presence device (perhaps the mobile app device), go into its page, and click into the "Events" button at the top to see history (for real time views, the "Current States" on the device page will be more helpful). "Logs" on the left side in the admin UI will also normally show you a history of what events happened when as long as you leave "Enable descriptionText logging" turned on for devices (as it is--and remains--by default, at least in stock drivers), though what appears here depends on the driver.
The lag with some of your automations could also be a few things. If they're Z-Wave devices, for example, your Z-Wave mesh might be weak. The presence of "ghost devices" is also known to wreak havoc: check your Settings > Z-Wave Details page for any items without anything in the "Device Class" column or possibly without an associated Hubitat device in the "Device" column (which isn't inherently problematic, but the "Discover" button you should see there instead will make one; if it gets added as a generic "Device" and you see nothing under inClusters, secureInClusters, and outClusters [all of them; one or two blank is fine] under "Device Details" on the device page, that could also be a ghost...this recently changed so I'm not sure what the best recommendation on how to find them is). A weak Zigbee mesh could also be problematic, as could mixing Zigbee bulbs (besides Sengled, and likely also newer bulbs that are anecdotally reported to behave better) on the same network as non-bulb devices.
Just a few ideas for some of the problems. If any of these ideas sound like promising leads and your own investigation doesn't reveal more, feel free to share more details about that part of your setup, and someone might have more ideas!