I think polyglot wins the prize... I think you have somehow had water / moisture / condensation within the cassette body.
Firstly, you are very welcome to return the film to us in the UK, when you buy any ILFORD product thats your absolute right and we will tell you what it is, as always its incredibly difficult to tell whats going on without seeing the actual negs, I cannot see any manufacturing defect that would cause any effect similar to this. As an FYI we never use tape in 35mm cassetted production, even on the master cut spools the tag that holds it in place is lost with the first 2m as that goes for QC processing tests before that individual master spool is cassetted.
Simon ILFORD Photo / HARMAN technology Limited :