Google optimize tag firing; but still showing error

Dear Fellow Google combatants,

I have been pulling my hair while helping a client set up an A/B test.

We keep getting the error: "Google analytics tracking code not found". Therefore, we cannot start the experiment. We installed the optimize tag (without triggers) through GTM; using the correct UA pageview tag. We setup the tag sequencing to fire the optimize tag before the pageview tag. The containers are correct, the UA property is correct, the experiment ID is correct.

We don't have ad-blockers or any other tag-blocking extensions setup.

When I check the GTM debug mode; I can see the optimize tag firing perfectly fine.

However, we still receive the error "analytics tracking code not found"
I am at the end of my means here.

Does anyone have any clue what could be going wrong here?

Thanks a million in advance.