DI Vessel Issue

[Frankenshine]

I get this issue after I have changed the resin in a DI vessel and am flowing water through for the first time only. When I flow water through - it trickles out the 'OUT' and pressure builds up in the 'IN' section. After a few seconds I see whats happening and take the hose out of the 'IN' and it blasts water out under pressure. I have filled the resin up the lower part of the DI Tanks neck - screwed down the riser properly too. Everything seems fine till I initially flow water through. Just wondered if anyone else has experienced this issue. Is there a something obvious I'm missing. Relative newb looking for an experienced opinion. Thanks for any advice.