Torrents pause on their own

[Rick1]

Mac OS 10.6.8
Transmission 2.82 (14160)

Torrents that were seeding are now paused.
I did not manually pause them.
They start seeding again when 'Resume Selected' or resume clicked on individual files.
Later others are paused, not the same ones as before so not specific torrent related.
No changes have been made to settings used for years.

Any idea what is going on, and how to correct problem?

[Rick1]

There was no such error in message log on torrents paused since my original post.
Only a few ones "torrent not registered with this tracker".
Titles not ones that were paused.