For me, the reported bug seems to be resolved when following the steps mentioned in my bug report.
But.... unfortunately the fixing seems to have triggered some new issues.
1. Now sometimes the missions tab stays completely empty as shown in Buffy´s screenshot and is not loading at all. That´s new - the missions tab opened with an broken layout as shown in my screenshot in the bug reprt, now it is completely blank when it happens. This has nothing to do with using gold (since I did not use any in these cases) and not necessarily with switching to the missions tab for the first mission of the new box - it just happens., I cannot provide the reproduction steps yet, and there is ´not enough time left to find them on Beta, sorry.
2. Sometimes switching to the missions tab and starting a mission will result in an error message stating that the mission does not belong to the player.
3. Sometimes the report stating a successful outcome of a mission is not displayed when switching to a world where the event window was open and a mission was completed, so that you only see the box tab and no report at all, or the report is only displayed for a split second before the event window jumps to the box tab. Does not seem to happen when the mission failed.
All three issues only seem to occur when you have more than one world tab open and are switching from world to world, with the event window (s) open in these worlds. All three issues will be resolved by closing the event window and opening it anew.