Ok that last one made no sense on so many levels.
Barry-now loses his memory so all the Barry's in the future also lose theirs? That would assume that he never got his memories back in order for that to work.
I would give them a pass on that by assuming that it affected him because he was in the same time period.
But Wally loses his power because Savitar 'forgot' to give it to him. That happened long before Barry loses his memories. That also means he should have also not recruited Frost because he would have forgotten who she was, or anything he ever did as Savitar if they use that logic.
Their cause and effect makes no sense most of the time where some things are affected by time travel and some are not.