I tried to migrate our WFA 2.1.0.70.32 W2K8R2 to 2.2.0.2.6 W2K12R2 with backup/Restore. No errors during these steps.
On new server each worflow executed failed with error:
'_x0004_', hexadecimal value 0x04, is an invalid character. Line 1, position 115.
Any idea of what's going wrong?