Nothing to do with Ilford.
Process Pan F+50 to Ilford's own published technical information, not third party references, until you are across the differences those alternate processing methodologies will impart on the film. A processing fault is the first thing that comes to mind.
The lines are not characteristic of humidity damage, which manifests as mixed blotchy areas. But the effect of humidity-damaged film varies enormously.
Very, very few people experience any difficulty with Pan F+50 post-exposure, and it is widely used where I am for landscape/scenic applications, as it the excellent variable speed ADOX CMS II 20.
It is important to process Pan F+ 50 reasonably promptly after exposure. Like ADOX CMS II 20, the film has short post-exposure latency.
The film can be refrigerated and frozen, and in the case of frozen storage, it must be allowed to fully reach room temperature without interference before use.