I had 8 copper blocks crafted them into ingots and crafted them into blocks 2 months later and I got 18

Duplicate of MC-213630, which is invalid. The recipe was changed. First you needed 9 ingots to craft one block, but in 20w46a was changed to only require 4 ingots. That is how you got more blocks. This is not a bug. See the comment by @unknown on that ticket.