I can't find any evidence that this is normal if you've never had any connection to the addresses. But you can get a connection to an address from just having mail redirected to it by Royal Mail.
An unexpected address can be a sign of identity fraud, perhaps in this case by your ex. Obviously only you can judge if that's a reasonable suspicion.
If your finances are now disentangled, you should be able to file a "notice of disassociation" from your ex and see if that makes the address disappear.
You can also just ask directly for the address to be removed. The credit reference agency would then contact the institution(s) that added it to get more information about where it came from.
Source for some of this: https://help.creditexpert.co.uk/help/sv635/Credit_report/linked_addresses