The result came on the back of a promising 1-1 draw against Shrewsbury and a 2-1 win over Rochdale, and means the Potteries club have still not been able to avoid defeat for more than two successive games all season.
Glover said: "We are here again. We can't seem to put two results together at home and it's very frustrating.
"We took the lead against the run of play and for a while we looked capable of getting a second. But we've conceded early in the second half and then given them the second goal. The ball should have been cleared and it wasn't.
"Our concentration levels are just not good enough. We defend okay for so long and then players switch off. It's another disappointment but I have to give Gillingham some credit because they played well and are making progress."