this is the #1 pain point of logseq. even when paying for their sync feature, it is very easy to lose your notes. smart merge is a step forward, make sure all of your devices have that on.
if you really need to work quickly back and forth between multiple devices (which I often do) - i find that i need to try to remember to not edit the same block. so if i have a notes block about AI on my PC, and i need to jump to my phone to take notes from a call, then make a new parent block so that the “smart merge” will keep them separate.
assuming that the information was captured at least once by the sync server, you can always manually go back and recover an old version. (see Equivalent of 'bak' folder for iOS?)