Same here. It may be related to adding a transition or effect, and it seems to happen on track 3 and higher. I don't remember seeing it on track 1 or 2.
If I see it happen, using Undo right then takes care of it, but if I don't notice the issue until later, I have to delete the clip and bring it in to the timeline again. One other option has been to unlink the audio and video and just delete the audio. Obviously that only works if you don't need the audio.
YouTube/optodata
DS365 | Win11 Pro | Ryzen 9 3950X | RTX 4070 Ti | 32GB RAM | 10TB SSDs | 5K+4K HDR monitors
Canon Vixia GX10 (4K 60p) | HF G30 (HD 60p) | Yi Action+ 4K | 360Fly 4K 360°