Here's my thinking on it, right or wrong. It obviously can't be involving what is recorded in Revelation 20 pertaining to the first resurrection if John hadn't even seen these visions yet. Duh! Right? IOW, they couldn't be trying to confuse anyone about Revelation 20 if Revelation 20 didn't even exist yet. Therefore, we can rule that out. What I'm thinking then, is this.
Matthew 27:51 And, behold, the veil of the temple was rent in twain from the top to the bottom; and the earth did quake, and the rocks rent;
52 And the graves were opened; and many bodies of the saints which slept arose,
53 And came out of the graves after his resurrection, and went into the holy city, and appeared unto many.
This resurrection event included Christ rising from the dead and also included many bodies of the saints rising from the dead. This is the resurrection event they are saying is in the past. The err is not with that since they would be correct that this resurrection event was in the past. The err would be that they were teaching no other bodily resurrection needs to take place in the future as well since it already took place in the past, thus fulfilled entirely.
Whether I'm right or wrong that's what tends to make the most sense to me. Therefore, assuming I might be right, one can't apply 2 Timothy 2:18 to anyone in our day and time except for maybe full Preterists. Certainly not to Amils, since Amils, regardless how they are interpreting Revelation 20:4-6, keeping in mind also, that when 2 Timothy 2:18 is meaning Revelation 20 didn't even exist yet, Amils are not even remotely insisting there is not a bodily resurrection event in the future, because it was already entirely fulfilled in the past when Christ and when the many bodies of saints rose, therefore, no one needs to also bodily rise in the future because everyone that was to rise bodily already rose 2000 years ago.