Tracker does not show up in SlimeVR server when there is only one tracker active.

[Zipra1]

When only one tracker is active, it will only show up in the SlimeVR server for a brief moment, rebooting it makes it track for another brief moment.
Having two or more trackers makes it function as normal.
If this issue occurs and a second tracker is turned on, both will start working.

[ShineBrightMeow]

You can try clearing on your Receiver and all of your Trackers, then try re-pairing them all again.