I think it your RAM memory issue in your workstation. What is the RAM and which processor are you using. The recommendation is 8GB RAM and Core i7 processor. I face this issue before when my workstation doesn't have enough RAM. I must say you assembly is heavy, and that is why it is causing this problem.
Another solution is, if your assembly contains too many components and subassemblies then try to make assembly light weight, or do speedpack for few assemblies which are not actually required for mating and referencing. It will drastically reduced the memory size of your assembly and thus your drawing might be updated easily.
It is very highly unlikely to be my RAM issue.
Using 16gb of DDR4 ram.
Intel I7-6700K CPU.
It occurs on any size assembly. Large and/or small...
Note, I think this only started happening when I installed SW2017 with SW2016 already existing on my PC.
Yes, you are right. But also try my another option i.e., whichever assembly is not required for mating purposes, just do speedpack for those assembly. It will drastically reduce memory size for you assembly. And parallel make other assemblies light weight. This also helps to further reduce the memory size of your assembly. Hope you know both this speedpack & Light weight. =]