It’s the “obvious”. I’ll cut out a small section of one of your screenshots to make it clear that this section of the +3.3V net is an isolated island and not connected to the rest of the same net:
This is often overlooked by beginners which don’t know what to look for.
And isn’t made any easier by the ambiguous message. I have suggested that the message should say “the net is split in several parts” or something like that.