Mallinder's men saw their four-match winning streak come to an end as they were beaten 29-24 at Kingsholm.
Gloucester scored five tries, taking advantage of some porous defending from the away side.
Saints did grab three tries of their own, with Jamie Gibson, Harry Mallinder and Mike Haywood all dotting down.
But Haywood's effort 10 minutes from time was only enough for a losing bonus point as Gloucester resisted a late fightback.
And Mallinder said: "It was very frustrating.
"It was an arm wrestle and, particularly in the first half, we never really got to grips, although there was some decent play at times.
"We never really seemed to get on the front foot like we've been doing over the last few weeks and we were slightly inaccurate which made it difficult.
"We came back and we nearly gave ourselves a chance, but it was a bit too late."
On his side's defending, Mallinder said: "There were some big moments and our restarts were disappointing. Credit to Gloucester there with their flat restart - they got a bit of success from that. It puts you under pressure and puts them on the front foot.
"We look at the defence from the scrums, they scored from two scrums, and the first one we need to do a lot better than that. In my view, a couple of our players couldn't get out, which is quite frustrating, but that's life."