I had a similar issue…
- Was in a project working on pattern and kit where I had customized the sounds.
- Saved kit, saved project, and switched to another project.
- Turned A4 off. Turned it back on about an hour later.
- Loaded project from step 1. Kit no longer had customized sounds. All custom sounds from the kit were gone and all sounds were default.
Tried to reproduce a couple of times but couldn’t.