Hi sunni77,
for me, the problem as i mentioned in the other thread (https://ww.wp.xz.cn/support/topic/widgets-not-saving-again?replies=20#post-5298045) was due to the interaction between WordPress and another CMS, SPIP, installed on the same server account. I installed WordPress on a subfolder while SPIP was installed at the root. SPIP had a special security screen (ecran_securite.php) which was in conflict with the Worpress widgets. Removing this security screen solved the problem.
You mention that your problem occurred after a hosting migration. Is your WP installation alone on the new domain?
I don’t think this is related to a particular version of WP.
Regards,
Pascal