I had similar issues across 3x HPE DL360p servers.
All the same configuration with 8Gb SD card. (Which HP has now replaced with a 16Gb card in quickspecs)
Always updated firmware's every time, and 2 -6 months later same issues. Also exhibit fan spin up and spin downs every frew min.
All the same configuration with 8Gb SD card. (Which HP has now replaced with a 16Gb card in quickspecs)
All storage is on SAN.
Check your ALt F12 on exsi console and you will see issues with bad blocks.
My end result. Removes SD Cards and installed hard disk. zero issues. since and faster boot times.
Conclusion. For SD cards their write cycles start going bad. to reset the SD card and full power drain on server is reuqired. but it will come back sooner and the SD card will eventually fail.
Remember that you need to point alllogging to other writable locations for the ESXi hosts. and off the SD card to keep IO low and static on the SD cards.