I just tried this on my little Ortur Laser Master next to me since it’s running GRBL also and could not reproduce your problem. I tried with my existing preferrences file and with an empty preferences setup just importing my Ortur device config and changing the default units to mm/s and turning the fire button back on. ie I did’t change anything settings but those two and got a decent circle.
I made the circle within Ortur using the circle drawing tool and then the offset tool to make a 3mm wide circle. I do see a gap in the design when I let it do “Flood Fill” as opposed to when I turn that off. Maybe you can try turning off flood fill in your layer setting on the Advanced tab?
The one by itself with the wiggles was from me having speed too fast and the whole wooden table my machine is on was swaying back and forth. It’s done with 0.9.24 along with the 2nd from the top where I slowed the speed down and rotated the scanning direction back to 0 deg. Others are from v0.9.21 and then back to 0.9.24 with clean slate config.