Hatsan Spark compressor not working???

[Ed24]

I have a Hatsan spark knock off.  Been using this compressor for about a year now and has always worked great.  Went to fill up a gun yesterday and its having an issue now.  Open the bleed valve, turn on the fan and then turn on the compressor.  It runs and pushes air just fine until you connect to a gun and starts to build pressure.  Around 200psi it starts to slow down until it stops around 600psi.  I'm thinking its building up back pressure.  Has anyone had this issue and repaired??