BUG? Urgent! Arduboat circling when arriving at a waypoint while logged waypoint distance value is static during Auto mission

I have an boat running a pixhawk with Ardurover V3.1.2 which has deveolped a problem that I urgently need to be resolved. Fast help would be very much appreciated.

It had been working fine for a while and now suddenly developed the problem that it will not continue to the next waypoint after reaching the current waypoint.
The symptom is that it will start doing circles passing through the same waypoint over and over again. If I manually switch forward to the next waypoint, the boat will approach the next waypoint and do the same.

From the logs I discovered, that the waypoint distance (WpDist) value will not change between waypoints. Only when I switch to the next waypoint or switch modes, there is step like change, but no gradual linear change when approaching the current waypoint. In a normal working mission the WpDist graph looks like sawteeth jumping to a high value which is then decreasing linearly to almost zero before switching to the next waypoint.

What could cause this behaviour and how can I resolve this?
If it is a bug that has already been addressed in an updated AR version (which I could not see from any release notes though), can I update without having to reconfigure navigation function parameters, since those functions have been changed since AR3.1.2 quite significantly as it seems?

Here is a link to the dataflash .bin log, so thank you to everyone taking their time to review and help me with this.