Check "Remove internal patches". You should get used to the way A:M extrudes and be aware of it, but sometimes if you miss it, it can be a good helper.
=> With nothing selected in the modeling window right-click and select "Remove internal patches". (see the attached video)
After that the internal patches should be selected and you can drag them out or delete them.
Best regards
*Fuchur*
feature_internal_patches.mp4