Sounds like a hub failure.
Did you run a zwave repair? This can take a while to propagate through your system, so you won’t necessarily see instant results as soon as the repair is finished, but if there is a network addressing issue, you should see improvements within a couple of hours.
Do you have any Devices which are directly associated to each other? That’s a separate zwave step that allows two Z wave devices to talk directly to each other without going through the hub. Most commonly used for a motion sensor and a light switch, or for a master light switch and then auxiliary light switch. Both devices would typically be in the same room. Direct association is usually used to remove lag.
If you do have any associated pairs you can test those. If they are also failing to talk to each other, then it’s not the hub, it would have to be some weird kind of local Interference. Sometimes you see this if someone gets a new baby monitor. If you’re in an apartment, this could even happen if your neighbors got the new baby monitor. But it’s less and less common as most baby monitors have moved off this frequency. But if you got one at a yard sale or pulled out an old one that you used when your kids were little and now your grandchildren are visiting it could happen.
But the most likely problem would be just that the Z wave antenna in the hub is failing.
What did smartthings support say?