I posted an issue to github, because I can’t seem to fathom what has caused this strange behaviour:
Running darktable 2.7.0~git1504.a4d5069cb (first upgrade in days or so) today,
darktable continually freezes up irrespective of --disable-opencl
Possible clue : output to terminal as below (for 21 distinct images)There are unassigned iop_order in the history!!! image: 55685 module: collect version: 1
Is anyone else finding difficult with the latest master?
Hello, no problems here with v2.7.0+1506~g3dd55316d-dirty, neither before.
Xubuntu 18.04.2
Do you have some usb device attached which might offer PTP protocol?
After numerous attempts at starting with different config dir and no lua folder, eventually determined that my database must have become corrupted. I have closed the issue on github, after successfully building a new database. Now to rebuild all the thumbnails (32k of them! 
)
Thanks for those who sought to help.
How did rebuild your database?
Hi David,
I renamed the existing one and started darktable; it created a blank one. I then imported all my raws and accompanying .xmp sidecars. Of course, this only works if you keep separate .xmps.
Unfortunately, custom settings in the darkroom and mapping modules are then lost.