Hi,
yesterday I did 3 easy and short bike rides, recorded with my Edge 530. In between the bike rides (after the first two, before the last), I did a 2x20min threshold running session with my Forerunner 965. Watch reported 55h of recovery time after this run (but it didn't know about the two prior rides at that point, as I hadn't synced watch or bike computer yet).
After the third bike ride I got home and synced my bike computer, but still didn't sync my watch yet, and went to bed. In the morning I synced the watch (sadly didn't check recovery hours before that), and my morning report told me I am fully recovered. Recovery time is 0h, with the 55h recovery work-out being only 15h ago! Garmin Connect also showing 0h recovery, so things are consistent (but wrong).
Wild speculation: Maybe True-Up between the bike computer rides (that surely were very easy and would have resulted in very low recovery hours) and the run somehow overwrote the run recovery time?
There are similar reports in the forum, e.g.:
This describes something very similar, with Forerunner 955 and Edge 830, about 1 year ago.