Hey @mattyg77,
I have reproduced the issue on version 6.0.0-rc2 on my local, and the issue seems to be of the configuration settings of the theme.
I have applied the settings you have mentioned in the screenshot attached and was also facing the same issue.
On some research I got to know that the cause of the issue is the "Fixed Position" Checkbox being enabled in your settings, under : "Header & Main Menu" > "Mobile Header" > "Fixed Position".Disable the option ( remove the check from the checkbox ) and save the settings, see if the issue still persists. As for me it was resolved after doing this.
If it works as mentioned we either need to change the issue summary and check the functioning of "Fixed Position".Please let me know if this works and anything else I can help with.
Thank you !