Glitched textures when switching from 1.9 to 2020.3

Hi, I recently switched from version 1.9 to 2020.3 because I wanted to continue my old mod. I obviously encountered a lot of bugs, and one of those were glitched textures. Some random textures just showed up like a glitched block and I dont know why because there are no particular relations or criteria for this to happen. I checked in the resources tab and said textures result with an exclamation point near them, does this mean they are damaged in some way? Also this happens with some json models, but only some of them, again with no particular criteria for this to happen. How can I fix these problems?