Like items not stacking
The Devs are aware and have posted a work-around for this issue. Place any ‘Account Bound on Acquire’ items in your inventory, and change maps. The items will now stack.
This works for most items.
Good luck.
Yup, already a known issue and being looked into: https://forum-en.gw2archive.eu/forum/support/bugs/Bugs-from-16th-Patch-Compiled