Hi,
I can confirm that there is an issue with FAN and "SMART_BANNER" since FAN SDK version 5.2.+. The current version is com.google.ads.mediation:facebook:5.4.0.0.
For some reason, I believe, the adapter is no longer matching the Admob banner sizes to the closest FAN banner sizes. And it's been like this for a while now.
I believe SMART_BANNERs would have a higher eCPM, so we really need the adapter to support those banners again please,
Regards