Many /tmp/6365733* files during TimeMachine backups

After I upgraded to BigSur, my /tmp folder started to fill up with lots of zero length files during TimeMachine backups. They won't go away automatically when backups are stopped.

% ls -la /private/tmp/63657330bbd*
-rw-------  1 root  wheel  0 13 фев 11:04 /private/tmp/63657330bbd8317c
-rw-------  1 root  wheel  0 13 фев 11:06 /private/tmp/63657330bbd87a44
-rw-------  1 root  wheel  0 13 фев 11:10 /private/tmp/63657330bbd8eae5
-rw-------  1 root  wheel  0 13 фев 11:12 /private/tmp/63657330bbd9240a

This is what I see when TimeMachine is working:

% sudo fs_usage | grep 6365733
11:04:25  open              private/tmp/63657330bbd8317c                                                     0.000566   fseventsd
11:04:25  open              private/tmp/63657330bbd8317c                                                     0.000091   fseventsd
11:04:25  open              private/tmp/63657330bbd8317c                                                     0.000065   fseventsd
11:04:30  lstat64           /System/Volumes/Data/private/tmp/63657330bbd8317c                                0.000021   fseventsd
11:06:25  open              private/tmp/63657330bbd87a44                                                     0.000219   fseventsd
11:06:25  open              private/tmp/63657330bbd87a44                                                     0.000056   fseventsd
11:06:25  open              private/tmp/63657330bbd87a44                                                     0.000044   fseventsd