I'm on OS X 10.9.5 and I have not been able to perform a backup since the upgrade. I decided to trace Control:Mac during a backup using the dtruss DTrace script. You can see the tail end of the trace until Control:Mac crashes here. My backup went through updating a few albums, but crashed trying to transfer the first of four new albums.

This part seems salient:

SNIP


rename("/Volumes/Data/MDMS Backup/media/album/27/a7/01010325d98a22585e42a66f702e4f0327a7/backupinfo.fse.atomic_tmp\0", "/Volumes/Data/MDMS Backup/media/album/27/a7/01010325d98a22585e42a66f702e4f0327a7/backupinfo.fse\0") = 0 0
psynch_cvwait(0x9EB328, 0x100000100, 0x0) = 0 0
psynch_cvsignal(0x1C97980, 0x100, 0x0) = 257 0
sendto_nocancel(0x5, 0x4271010, 0x10F) = 271 0
sendto_nocancel(0x17, 0x4302010, 0x28) = 40 0
gettimeofday(0xB10009E0, 0x0, 0x28) = 1428415335 0
workq_kernreturn(0x20, 0x0, 0x1) = 0 0
psynch_cvwait(0x1C97A78, 0x100000100, 0x0) = -1 Err#316
gettimeofday(0xB10009E0, 0x0, 0x0) = 1428415335 0
write_nocancel(0x2, "\nUnhandled Exception: System.ArgumentException: The requested value 'Tidal' was not found.\n at System.Enum.Parse (System.Type enumType, System.String value, Boolean ignoreCase) [0x00000] in <filename unknown>:0 \n at Sooloos.Msg.Durable.TrackFileInfo.SetF", 0x400) = 1024 0
write_nocancel(0x2, ".Boolean& isFinal) [0x00000] in <filename unknown>:0 \n at Messaging.FSEMessageDecoder.DecodeOneMessage (IMessage m, System.Int32& requestId, System.Boolean& isFinal) [0x00000] in <filename unknown>:0 \n at Messaging.FSEMessageDecoder.DecodeCommon (System.", 0x27C) = 636 0
munmap(0x147FD000, 0x1000) = 0 0


/SNIP

The album at the top of this snippet is one I imported from CD yesterday, so I'm not sure exactly the error message that follows is related. (incomplete) Tidal integration may be the cause here. One thing that seems worth trying is removing all Tidal albums in the Library to see if that makes a difference.

Edit: just passed this on to my PP as well.

Soundserge

Antipodes CX + Roon, 818v3, DSP 7200SEs, 218, DSP3200s