Steps to reproduce the issue

None

Expected result

Keeps enabled

Actual result

Goes disabled

System information (as much as possible)

Has happened since version 3.8.

Additional comments

Core Update site goes randomly (?) to disabled state and has to be enabled manually, after that update works as expected. However, update drops back to disabled and I haven't found any logical reason for this. Periods between version updates are quite long, so I cannot say whether it drops on next day or next month.
When 4.2.9 was released, I enabled update (once again) and when logged in today, Joomla told me it was still 4.2.9 and up-to-date, but the latest version currently is 4.3.1.