METAR bubbles is a known issue since SU7 1 year ago. There are some existing posts in the weather bug forum, the main one is : METAR keeps disrupting the weather/ bugged weather/Cumulus/CB clouds only/no medium to high cloud coverage
You can post your comments there, no need to open a new one.
Maybe you are right regarding the haz coming from METAR, this has been implemented since SU10 I guess.
Also you only experience that with live weather since METAR only exists there, it is not in presets neither custom weather.