Win10, six-core i7, 32GB RAM, 1060 GPU, running on something like 6 internal 'disks' all but one SSD.
I manually save every major step done, really ... so what, 3-12 minutes apart? ... and do iterative saves (save-as) every couple hours or so.
Rarely have crashes. Mostly if there's an issue with a new build, get it sorted over a few days at most, then just ... work.
So I feel pain for your situation ... that would really be ... painful.
Hope you're filing over on the UserVoice system ... with full data on what's going on. They are putting more emphasis on nailing some of the bugs that hit people these days, and that gets the data to the QC engineers directly. Some things are really hard to replicate, and when you get a rig that's having such issues, it can at times be useful to get more data on it. And I know of a number of times engineers have come on over there and asked for even private discussions which would seem to indicate they wanted to see what was going on.
So ... I can't replicate your behaviors, but think it's important you keep a record of this posted over on the UserVoice system. This forum is primarily user-to-user help, the engineers look at the UserVoice stuff.
Adobe UserVoice Bug /Feature form: https://adobe-video.uservoice.com/forums/911233-premiere-pro
One thing that I have seen mentioned by "some" people with problems is that Win10 updates can require an update from the vendor for your nvidia or amd card... and that there are times when a new video driver can cause problems that are fixed by going back to an earlier driver from the vendor\
You don't mention your video card (nvidia or amd) but have you tried a different device driver from the vendor?
I don't push my system, so my absence of crashes is not really comparable. Older i7 Win10. But I've been burned over the years with less stable versions. And, in any event, any user with a stable system can lose a hard drive and Bam! - nightmare begins.
As Neil, I save after every significant change. I use "save a copy" for my primary iteration copies (to a different drive), again doing that "save a copy" after significant changes. Those saves are probably influenced a bit more by thinking "how bad will it be if I lose my primary file"? The harder it would be to recreate from the last "save a copy" version, the more likely I'll make that manual backup.
Most of my projects currently are small. Larger projects make all this more painful (as in saves take longer; autosaves are more distruptive, etc).
Yes, I use autosave. I tested it recently, and a) it works pretty much as described in the latest documentation (it has changed in the past few years) and b) using "save a copy," I'm not sure when I would actually rely on it. It I were doing more large projects, I'd consider making it save times much longer to avoid disruption. I really don't rely on it.
I started using the cloud sync, and it can be useful, particularly for a local, multidrive disaster. (Computers can still be zapped by lightnight.) But the basic sync saves ONLY the last version saved. Both a manual save or autosave triggers the cloud copy. Of more value is the fact that "save as" and "save a copy" both trigger a cloud save of that new project file. So the manual save a copy or save as are keeping those iterated versions in the cloud, not just on the local computer.
I follow my own advice in Step 4 below and I can't recall the last time Premiere Pro crashed on me.
Full disclosure, however, requires me to say that I have switched over to DaVinci Resolve for my post production work. The last version of PP I used for a real project was 2017. However, I've had no troubles opening up and playing around with older projects in 2018 up to version 12.1.1. (My subscription expired before I could test 12.1.2.)
For those with lesser experiences, here are a couple improvements Adobe could make to help.
I am also using Davinci Resolve 15 more (Free Version). They are now up to Beta Version 8. Their User Forum still reports many bugs. I have used many video editing programs. They all have bugs.