Tested on V9.0 and PSA solution 18.104.22.168.
I made some findings regarding Fixed Price lines when running Batch Job, "ProcessRunner":
- Set Milestone to date -> leave Milestone at "Not Ready for invoicing" -> run Batch Job, ProcessRunner -> invoice created at value 0 -> delete invoice -> set Milestone "Ready for invoicing" -> run Batch Job, ProcessRunner -> NO invoice is created.
In order get the Batch Job to recreate the invoice, the Milestone has to be created again. Then setting it at "Ready for invoicing" and running the Batch Job creates an invoice with proper sums.
I don't know if this is intended or not but just thought I'd bring it up. With the T&M lines all I had to do was set "Milestone Status" to "Not run" and I was able to recreate an invoice with proper sums.