Hi, we have experimented something similar in 7.14.6 but, for now, we can’t reproduce it.
We found there is this issue regarding the reset of the timezone if a user bean is saved: Users save() method always sets the 'timezone' to 'UTC' · Issue #10494 · salesagility/SuiteCRM · GitHub
If someone is able to reproduce the problem stated in this topic and try the patch suggested in the linked PR Fix #10494 - Users save() method always sets the 'timezone' to 'UTC' by serhiisamko091184 · Pull Request #10569 · salesagility/SuiteCRM · GitHub, it could be great.