[itsme]

In "ABC workflow - Freude schoener Goetterfunken" https://www.zubersoft.com/mobilesheets/f...12171.html I also showed my complete workflow. The difference to your workflow is that I used the plugin ABCImpExp V1.1 to create the ABC file. This avoids the need to create an intermediate MusicXml file and import that into EasyABC or Michael Eskins tool to create an ABC file. 
The resulting ABC files of the three methods are probably different. It might be interesting to compare them in detail.

I used "Freude schoener Goetterfunken" as my example because it's out of copyright (and I already had it and need it in different keys).

Your transposing issue in MobileSheets is already described:
"I had to add the ChordPro chord [F] before the ABC section to tell MobileSheets what key we're in. This is not only used to fill the "keys" field in the database during import, but also required as the starting key for transposing. MobileSheets could have detected the key from K:F in the ABC section."
If you import Hay_Burner_Test_2.pro it is correctly shown with key=F and transposed by MobileSheets just fine.
Still a bug that needs to be fixed, but the workaround is easy an feasible.