I had a similar issue…

  1. Was in a project working on pattern and kit where I had customized the sounds.
  2. Saved kit, saved project, and switched to another project.
  3. Turned A4 off. Turned it back on about an hour later.
  4. 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.