Too much back pressure being generated by that spray nozzle. Whoever built the xjet doesn’t know what they’re doing, and put something sized too small for the orifice inside.
If you do a search, you can find people’s modified xjets where they replace the stock nozzle with quick connects to use whatever nozzles or jrod they want.
Also, their upgrade kit is a joke. So much stainless steel, on something meant to handle straight bleach, is asking for trouble. Those quick connects and valve will be junk in no time. Should’ve been all plastic fittings.
And don’t get me started on that basket strainer. Just, no.