So we have a film that needs development very promptly after exposure and gives a problem with flash. Ditch this film's production is what I say Simon Galley

Seriously as per the loss of latent image problem I have never heard of problems peculiar to flash either.

I don't know what the cause of the OP's problem is but I very much doubt an inherent flash issue with Pan F compared to other films

I think the OP needs to be steered towards other likely causes