I have 2 Kwikset Z-Wave Plus locks in service. (I'm not sure the model number matters, since the same generation appears to all use the same card, but if it does, I have 910s.) The first thing they need is a good , no great , wait, perfect mesh. (And even then, the mysterious Z-Wave routing still comes into play.) So, if you want to stick with Z-Wave, get your mesh solid. (I didn't read every post of this thread in detail, so if yours is already solid, then great!) The other thing -and there are other threads out there that talk about this- is that the Kwikset Zigbee implementation doesn't play as well with HE as the Z-Wave does. It's just little things in the driver like double reporting, and something else that doesn't come to mind at the moment, but for me, at least, it wasn't as simple as swap the cards and done. There are, again for me, trade-offs. If you do want a Zigbee card, though, as you mention, there are cards available relatively inexpensively. Check out this thread:
Or, for the TL;DR version, hop over to Amazon and buy the cheapest one of these you can find used (search the different colors/finishes) from the Amazon Warehouse and harvest the Zigbee card from it.
https://www.amazon.com/gp/product/B071KLHWSP
IME, yes, you need to space out commands to avoid overwhelming either your mesh in general or the lock itself. I'm not so sure it isn't a HE software problem, as it just popped up for me one day (somewhere close to an update,) but I have multiple rules that fire with lock changes and they did get bogged down. I found that adding some delays in the rules to spread things out helped tremendously. I don't think the triggering is what hurts, it's the multiple simultaneous actions, but I didn't tinker that much. The delays fixed it, so I left it at that.
