Last year, there was a Zeal of Zenithar bug to the effect that certain items found in stolen boxes could not be laundered. E.g., I still have a lonely stolen Group Repair Kit in my inventory a year later, and I've tried laundering it within the past couple weeks.
Various examples of the bug were reported at the time in
https://forums.elderscrollsonline.com/en/discussion/609832/cannot-launder-certain-items-from-the-stolen-zenithar-boxes I think you actually fixed it with respect to Vault Keys, but not other items (such as Group Repair Kits).
Since I play mainly on PC/NA, I can't test directly on the PTS whether you've finally fixed this entirely. And stealing or raiding Thieves Troves on the PTS until a box was found would be slow and tedious. I.e., this will be hard for players to test for you. So please be so kind as to take extra care in testing it yourselves!
Thanks!