Wow. It seems I found the problem and the fix…
opkg install --force-reinstall libevent2
“verbosity 4” logs of unbound, the “only untouched component” used only by unbound and the “iftop” oddities reported here told me to give it a try.
And to answer the obvious question… my eMMC says it’s not dead yet:
eMMC Life Time Estimation A [EXT_CSD_DEVICE_LIFE_TIME_EST_TYP_A]: 0x01
eMMC Life Time Estimation B [EXT_CSD_DEVICE_LIFE_TIME_EST_TYP_B]: 0x04
eMMC Pre EOL information [EXT_CSD_PRE_EOL_INFO]: 0x01
And “btrfs scrub” didn’t report errors either.
unbound 1.19.3 up&running now. Would be nice of the turris people if they can provide it upstream as well since there are CVEs for lower versions.