I have noticed this degradation of 5.5 reliability to what, in my experience, I consider Claude-level of reliability since early June.

My journey dealing with this has been transitioning from 5.5 high to 5.5 xhigh to 5.4 high.

5.4 high has been perfectly reliable for me for the last 3 weeks, and I am happy there.

Occasionally, I run some tasks on 5.5 xhigh to check if it has gone back to being 100% perfectly reliable, but, at this point, I am assuming they are just counting on releasing 5.6 rather than dealing with this reliability issue.