HLG footage looks wrong in 10.4
I was editing a bit of video filmed on a Sony PXW-150 camera it was 1080 50p HLG and it looks totally fine in FCPX 10.3.4 using a Wide Gamut library and a REC2020 Project. but when I upgraded the same footage into FCPX 10.4 with a Wide Gamut Library and a library set to REC2020 HLG all the colours look different compared to 10.3.4.
this happens when I upgrade a 10.3.4 library or import the footage directly into a 10.4 library. FCPX10.4 can tell the footage is HLG but won't display or export it correctly.
is there a setting I'm missing? I tried to colour correct the footage but when it looks correct on the viewer it looks awful when exported using either Compressor or FCPX
I'm editing on a Mac Pro 2013 with High Sierra 10.13.2 with 32gb of ram with a cinema display monitor.
many thanks for any help with this.