Vanilla unstackable items are stacked using EssentialsX and placed into a shulker.
After placing, breaking, and replacing said shulker in survival mode, the items will unstack and delete any other items in that chest.
This did not happen prior to 1.14. (That is around when we started noticing it happen.)
Thank you for your report!
We're tracking this issue in MC-170536, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki
-- I am a bot. This action was performed automatically! Please report any issues on Discord or Reddit