Yes, this will be quickly resolved at the airport and I wouldn't add much or even any extra time for it.

There may not be a next time since the restrictions are believed to be ending in May, but if you have a connecting flight you need to avoid doing the Manage My Booking upload in the first instance, and in any case you only get one go at it. So here is the step by step guide, which may take a few seconds to load:
https://www.flyertalk.com/forum/brit...l#post34983129
and the other related thread, which will show that you are far from alone in having these issues:
https://www.flyertalk.com/forum/brit...periences.html