Glue for internal rubber seals on uPVC windows

The only thing I can see working here with rubber and vinyl would be cyanoacrylate (super glue). There may be other options, but that gets into product recommendation territory.

I'd use a gel type that will stay put and not flow everywhere. Take the sashes out to a clean, stable work area if possible, and consider masking sensitive areas first.

Do be sure that you're actually seeing pull-off and not tearing of something that's set into a channel, for example. Replacing the entire seal in the latter case may be the only reliable option.