Hi,
I've noticed that if you group layers within your web map, when you open the layers list in Field Maps the groups also have to be turned on/off (rather then just expanded). (how this works doesn't see intuitive see separate post Display of the layers list within Field Maps - Esri Community)
Turning off a group though seems to hide all the sub layers in that group from the map (as I'd expect) (irrespective of whether the individual layers are turned off or not). However if you untick this group layer and then go to add data to the map these sub layers are still shown in the layers available in the 'Collect' panel of layers (if they were not individually turned off). This feels wrong, as if you've turned these layers off via the group and can't see them on the map, then you shouldn't be able to still collect data against them.