Could be uniq is removing similar lines.
Try something along the lines of:
journalctl --since="2012-10-30 18:17:16" --output=cat --grep='BTRFS .* i/o error' | less
from Identify damaged files - ArchWiki
and fix the more recently detected errors first.
I don’t know on fedora, but Debian and Arch package managers have this feature where they can verify all installed package files match their package checksums. I’m sure Fedora has the same thing, try that first… even if it crashes half way through, it’ll be useful info for you.
Also, consider adding some crons to check journals for different types of problems and have it email you a report. (In case things degrade further).