Hello GerSheph,
I see the issue in your video. While selecting the "fog" layer you unknowingly change from ECWMF model to the ICON model. Hence when you select "low clouds" afterwards, it's showing you the "low clouds" from ICON. For some reason it again changes back to ECMWF when selecting the "cloudbase" layer and with it you see your original "low cloud" data. Only the ICON models (ICON, ICON-EU and ICON-D2) plus UKV-model have the "fog" layer. So Windy will always change the model when you request the "fog" layer.
Kind regards,
Mark