User blog comment:KodachiZero/Chain Chronicle V3 on the Wiki + Q&A/@comment-27837128-20161126181233/@comment-26432452-20161126230455

Your old weapons/enhancers/forgers are still be counted. Only new enhancers etc that you get at v3 will not counted to your arcana limit.

One more thing about this that if you use something like enhacers/forgers, it will be taken from your newest one instead of your oldest enhancers that still stucked at your arcana limit. Like if you have 3 5* enhancers before v3 then you add another 2 5* enhancers. they all will be stacked but your 3 old enhancers will still be counted until you use them. If you use them to your units, you will use your newest enhancer first until they are gone then the old one.

Try use all your enhancers first before add a new one or sell an old weapon that you know it was from before v3.