Thunderbird Threads from different conversations are mixed together in my folders.

Hi, I'm struggling to resolve an issue that I noticed when organizing my emails all into individualized folders. Somehow my threads are mixing together different conversations, as demonstrated in the image attached. I've tried right clicking the properties and "repairing" the folder but that did not have an effect. I'm new to Thunderbird so perhaps I am doing something wrong that is obvious.

Any help is appreciated