thanks for the log, but unfortunately it does have enough details. Whenever you have an weird behavior from B3 and want to understand what's going on, you have to lower the B3 loglevel down to 9 (or even 8). if the log level is higher, then it won't be useful to us.
Anyway, I've been investigating and found out the issue. This is fixed in the B3 Metabans plugin v0.5.
Also 0.5 fix an issue with ban duration. In v0.4.x B3 ban durations (which are in minute) were not converted to seconds before being sent to metabans (as metabans expects). As a result, If you previously sent a B3 ban of 2 minutes, then metabans would receive a ban of 2 seconds only.
To fix that, just use the !metabanssync command again and all active bans will be sent again, but with proper duration this time.