I have rpi4 with 8Gb of ram for context.

I think it's just not a powerful enough unit to handle the load of X number of apps on said device. from bitcoind, electrum server, wallet software, to lightning nodes. I just think it's weak hardware.

I usually notice when I check my mempool and it isn't synced. usually the umbrel is still on & running but some service (not sure which I haven't investigated that far), sort of halts things up. my guess is its bitcoind (running umbrel w tor), as I have noticed when my umbrel halts, I usually don't have any active peers for bitcoin to talk to.

to fix I ssh into my umbrel and reset it from the console, and usually everything js resynced within 20 minutes.

I don't use this to route lightning because it is too unreliable.

a longer term solution is using a slightly old thin client office computer with an i5 processor and 8-16Gb of ram. I think node software packages are good starter kits, but should probably be run on beefier hardware - or install just the essential tools for your node on a clean debian/ubuntu install