I think it was the lack of social interaction that caused it for me. I did have a bit of social anxity when I started to hang out with people again last year. My stammering has however gotten a lot better since that time, now I try to focus on the content of what I say instead of how fluent my speech is. It did however take a lot of self reflection and good conversions with friends and a psychologist to come to that realization. I do however still stammer more in stressful situations.