Hi Lande
I think it could be due to some issue with your code.Pl remove your BADI /IWPGW/BADI_TGW_TASK_DATA implementation and then try again.
Also see if any implementation in BADI /IWPGW/IF_TGW_TASK_QUERY
Also check if this note is applicable for you
2299362 - BADI implementation of /IWPGW/BADI_TGW_TASK_DATA returns wrong values in case of $expand request
Refer a doc I had written sometime back
Additional info on S2 View / S3 View In Fiori Apps
Let me know if it helps
Regards
Vinita