Almost all cards are suddenly unimplemented for me!

Hey! I'm having a weird issue with forge 1.6.27 where almost all cards are unimplemented. Using the audit feature shows a varying number of unimplemented cards that changes every time I start the game, but it's always in the 20,000 - 23,000 unimplemented cards range. This, of course, breaks everything. The cards are in the cardsfolder.zip as expected and I can open the individual card .txt files just fine. And I'm sure that I played on 1.6.27 just fine a month ago or so, but don't know what I did to cause this problem, and redownloading it has not helped. Any ideas?