I had read about a problem with the new app where a scene with both switches and dimmers misbehaved. IIRC, dimmers would get switched on but level was not getting set.
This problem seems to be fixed in the current version (Nov 6, 2018 update) of the STSC app. On Android, at least.
I had one scene that had this problem and worked around it using a virtual switch plus Smart Lighting to control the dimmers.
Was creating another scene today with a mixture of dimmers and switches so I decided to see if the problem was still there. Had no issues!9