My Hammer Button Assembly also snapped and I too suffered power loss.
It was nearly sent back to Air Arms but they told me that a replacement Hammer Button Assembly was not available as they have been on back-order since October 2023! So I decided to hang fire on returning my pistol to Air Arms.

I contacted Air Arms only last week and they still can’t promise a delivery date for a replacement Hammer Button Assembly.

I got a friend with a lathe to make a replacement and as soon as the part was fitted the power was restored.
I guess that the hammer bounces without the complete button being present and this causes the dramatic power loss?