Hi,
My system: Rather old laptop with 8GB RAM, CPU Intel Core i3 M350 and an Graphics card ATI Mobility Radeon HD 5000 Series.
Running Windows 10
Just today, after todays zwift upgrade, zwift is crashing after less than 4 minutes of riding. It’s completely unusuable for me now. Yesterday it worked perfectly for a 60+ minute workout, and had 90+ minutes sessions in the last weeks.
Any ideas? So frustrating to have a have an update to make it completely unusuable 
I’d probably try a clean reinstall first. Plus installing any Windows updates, and any Radeon driver updates available on the AMD website.
Looking at the few reports in zwiftalizer.com relating to performance on the M 350 + HD 5000, it looks like using game resolution set to 576 may be necessary to avoid truly horrible frame rates. It’s not really good enough for Zwift. Performance worse than a phone.
Today it allowed me to complete the Big Ring route.
I did not change anything, I did not do a clean reinstall since yesterday and I did not apply any windows or driver updates. This morning I first wanted to reproduce the issue I encountered yesterday just for completeness, but it simply worked. I left it running and crashed after about 2h because of a different memory issue I posted in an other post.
By the way, yesterday I did try to restart the computer several times, getting crashes at the start of the ride.
So hope it was something temporary somehow related to the upgrade?!?
Regarding the performance of my setup, yes I’m aware of its limitations, but with an ssd hd and enough ram everything works reasonably well for me. I have it on 720p resolution and I’m happy with that.