Cats have started peeing on the doormat

[Romcom]

We have two female neutered cats, 8 years old, previously well trained. After one had cystitis and weed on the doormat, we are having problems with repeat offending. Both now well, they have both a cat flap and a litter tray. Litter is clean and in its usual place. No change of brand. Bought a new doormat which was a waste of £ as they just keep doing it.
Any ideas? Tried pet behave etc. It's only happening every couple of weeks.

Two cats need three trays really. Have you tried giving them cystease? You can buy it online to stop cystitis recurring.

Is there a new cat on the block, who they feel is threatening their territory?
Hence they feel that they have to keep marking the boundary?

Try putting their bed if they have one there. One of mine is doing it on the sofa and that is the only thing that has stopped it.

Not that I know of. We live on a street with hundreds of cats!