Containers aren't supported in Private Windows. Before version 1.7 TC manually disabled itself in Private Windows, with version 1.7 it now relies on the Firefox Manifest "incognito: not_allowed" so it doesn't run at all in Private Windows. If you experience problems with pages loading in Private Windows while TC is active, I'd encourage you to report it to bugzilla.mozilla.org.

Might want to try in a fresh profile (about:profiles) as well, to make sure it isn't a custom configuration influencing the behavior, like also happened here: https://github.com/stoically/temporary-containers/issues/331