You're right Jim, that's it! If the mount is tracking, there's actually no real problem or consequences, except that you're forced to use the ST4 cable instead of pulse guiding, but if the jump happens during the slewing that's a real problem becase the mount movement goes out of control! It happened a lot of times during plate solving, and that's a problem because instead of micromovements done for correcting very small arcsec the mount starts slewing on larger distances, or also if it happens during near the meridian flip it can trigger it. What can be done?
Due to this discussion, i tried to go back to ST4 guiding. My calibration with eqmod looks a bit messy, with some clusters of points near the center, while it for ST4 looks very nice and with a perfect right angle. There guiding also seemed to be a bit better with ST4, but not much so it could just be me looking for gremlins....
I don't know what can be the advantage for ST4 or pulse guiding but for me there are real problems on slewing. Anyway there are people that suggests that ST4 is better but so the contrary...
After a mount change, from EQ5 to HEQ5, and a EQMod cable change, the jumps remain... What can it be? A USB problem on the RPi4? I really don't know what else to think...