Or, What I Spent My Christmas Eve Googling, All In One Place:
TL;DR: add this build post-processor to your project: SymolicationEnabler unity post-processor · GitHub. Then for any crashes, download the dSYM and ipa files, put them somewhere Spotlight can find them, and the dumps in the Devices view of Xcode should symbolicate themselves.
Thanks Andrew, very useful post!
Brilliant description @andrew-fray ! Big thanks! 
UCB already generates dSYM files for you, so there is not need to add the post process build script to the project anymore except you require additional parameters. Therefore, and for consistency I have adjusted your guide a little bit:
The guide can now be found here: https://support.unity3d.com/hc/en-us/articles/208593736
Cheers @David-Berger - have there been recent changes? I think when I was trying this last month I could get a dSYM from UCB, but it was by default stripping useful symbols from the build. The SymbolicationEnabler fixed that. However it could also have been spotlight being slow to catch up, and out-of-date google’d info.
No changes. Probably spotlight was slow. But in the end you should not need it 
Maybe you have time to try it with your project again and remove your post process script and report if you still encounter problems or if it works now!
Nice summary, thanks!
My blocking situation is that I am using a remote Mac service through Remote Desktop from a Windows computer, so I cannot attach my device to that remote Mac. In this case I can’t see any devices in the Organizer/Devices window, only that Mac and the simulators, so I can’t follow your checklist from the part I quoted.
Could you suggest a way to still examine the crash reports on the remote Mac or elsewhere?
Also, what to do if a I get a crash report from a tester? Naturally, I won’t have that device inside the Devices window.
For Windows I recently found the free “iOS Crash Log Tool”, which lets you view symbolicated iOS crash logs on Windows. It’s very easy to use. Best of all, I don’t need to use my Mac to read the crash logs any more!
I don’t see the ‘Download .dsym’ option anywhere in Unity Cloud Build, as referenced in the guide. Did it move somewhere else?