I know this sounds daft ….but you say it triggers a sounder via the alarm system ? Was it set to a zone with chime ? And chime is now turned off ….a picture of what is being used would help
How old is it ? Shark are excellent in sorting any issues if in warranty ( 5 year I think ) we had an issue with ours and they sent out a replacement head within a couple of days …can’t fault them
A bell systems 203 strike ( AC ) is 30ohms …a DC strike is around 8ohms but I’ve known DC strike to be as high as 70ohms failed locked and failed unlocked …
The strike will only have the correct voltage when you activate the door release …are you measuring the voltage when you activate the door open button on your monitor ? …also try it with the release disconnected it won’t be voltage drop on that cable at that distance ….more than likely you have...