Class 2 NI - Under Small Profits Threshold

Storcko14

My OH has a small business and filed their 24/25 tax return this week.  On the completed return it showed a liability for Class 2 NI of £92.  My understanding is that Class 2 is optional if profits fall under SPT which is the case.  Although it's always been my OH's intention to pay the optional NI contribution, I was surprised to see it presented as an amount due and for a smaller amount than the standard Class 2 rate. I know that there was an HMRC IT issue earlier this year relating to Class 2 NI but I understood that had been fixed.  Can anyone shed any light?  Thanks