There is a bug in the MIDI Setup which you might be experiencing, and this is the correct fix. The MIDI device that shows up in MIDI Setup when no USB devices are plugged in (Midi Through Port-0) should not be in there (this is the bug), it should really just say ‘None’ or ‘None connected’ or whatever. If you select it (and unfortunately you don’t have a choice not to once you press ‘MIDI Device’), there is a loop created from the input of the patch to the output. In many patches MIDI clock gets passed through, so a feedback loop begins and tempo goes wild. The fix is to select a different MIDI device, but you have to have one to plug in. (there is also another fix, you can edit or remove the patch_loaded.sh file on the root level of USB or SD card). This might explain the problems on TRS MIDI.
MIDI clock is a steady stream of messages, 24 of them per quarter note. While these messages may drift a little, overall the clock will stay synchronized with the master, as long as none of the messages are actually dropped. The deviation you are seeing in tempo is most likely a display issue, i.e. rounding error. For example the master is sending clock at 100.7 BPM, one slave might round down and display 100, another might say 101, but if they are receiving all the clock messages and using those messages to drive sequencers or arpeggiators, everything should remain in sync.