I’m going to guess (about 95% sure) that this is a heat creep issue. I’d start with upgrading your Dual Extruder V3 to a Dual Extruder 3.1.
You could also take a look at this topic, https://forum.lulzbot.com/t/dual-v3-a-review-wait-for-v4-heat-creep-still-a-problem/6017. Instead of a 3.1 conversion, I went with printing and installing the fan duct I described in that topic.