I just tried to check for updates using iMazing (both v3.5.5 and v3.6.2) and get an error. This usually means that Apple has changed the authentication on their servers and iMazing will need to release an update.
Have you sent a bug report to iMazing? (I did; more reports are useful)
Changes to Apple’s systems are likely as the cause of iMazing’s issue, I’d say, in light of a recently fixed problem with Apple Configurator. Configurator was unable to log into Apple Accounts for several weeks, which affected installing and updating apps.