Just that: the 363 ( only) has no alternative liveries showing in either Timetable mode or Scenario Planner. No other locos are affected - they're all fine.
That's right, I think DTG already knows the problem and with the next update it will be fixed. It only can be a UI setting error at the RSN route, because the custom liveries for the BR363 aren't deleted.
I am wondering if this is because we have a TSW2-native loco mated to a Preserved Collection route. In other words, the 363 and its uacns wagons are LD-compatible, but the RSN route itself has not yet been made so. In other words, the route's menu draw routine should have an instruction "look for LD files," but of course that wasn't present in TSW2020 so it still isn't. OTOH, I don't hear of this problem occurring with the BR Blue locos, intruded into GWE. Unless the requisite "alt timetable" UI mod went ahead and handled the livery matter as well.