The user on whose account the problem was detected:
Oroborus

Coordinates:
[1111:815:2] (⌀17)

Date or time of the incident (according to server time):
I select to copy the property data from the fleets themselves:
Your fleet 24
, started from coordinates [1111:815:2] 29 Jul 2026 20:41:27 (Server time) sent to coordinates [1111:815:2] with order Recycling (0 metal, 0 minerals, 0 Vespene) will reach its target in 29 Jul 2026 20:55:07 (Server time)
Your fleet 1
, started from coordinates [1111:815:2] 29 Jul 2026 23:12:30 (Server time) sent to coordinates [1111:815:2] with order Recycling (0 metal, 0 minerals, 0 Vespene) will reach its target in 29 Jul 2026 23:19:49 (Server time)
Description:
In fact, it seem the actions described are not entirely correct. The fleet #24 was send from [1111:815:2] (⌀17) to my colony at [1111:815:2] with mission "Transport" where I sendt mostly metal and some minerals. When it returned it was supposed to merge again with the recycling fleet but got stuck. I did not realize this until after the second fleet (1) got stuck. That fleet was sent from the same [1111:815:2] (⌀17) with mission "Defense" for 12h at [1112:814:1] and did a free flight before I manually recalled it.

Actions required to repeat the problem:
Unknown if it will repeat? It somewhat did twice here, but normally this has worked without any issues.

Screenshot:

Upper line - original recycling fleet.
Middle line: - first transport fleet transport resources (should have merged with original fleet but did not)
Lower line: - defense mission with free flight before manual return (should have merged with original fleet but did not)