Cardigan sleeve help? Why am I getting mysterious extra stitches each round?

Hi crochet friends

I am working on a cardigan as a baby shower gift. It was going really well until the sleeves and now it’s driving me crazy.

Every turned round I seem to be adding a stitch somehow, so it starts to flare out. I’m definitely not doing any accidental increases, it must be at the end/start/turn? I’m not a complete beginner, but this is my first time working in turned rounds as opposed to in the round.

Pattern is:

ch1, hhdc all, slst to the first. (28) Turn. Repeat until required length.

Pattern also generally states - Working in the first stitch the ch1 does not count as a stitch so always ch1 and hhdc or sc in the first stitch.

So I’ve been marking the ch1 with a stitch marker, so I can skip this and then slst to the first? but I seem to have an extra stitch somehow???? This round I’m up to 30?? Supposed to be 28?!

I’ve redone this sleeve about 4 times now so any help would be much appreciated!

Pattern is the Ayla Cardigan by Baby Crochet Designs

Thank you!