Hi Niels,
This is a known issue to the TBC team. Some SPJ files are no longer importing in TBC 5.20 which imported correctly in 5.10. It is still possible to view these work orders in the Work Order Viewer (in both SCS Data Manager and TBC), though this is far from a complete workaround.
It's not yet known whether we will be releasing a patch to fix this bug, but I'll let you know if anything is decided.
-Josh