I read the paper and while I agree that maybe math is not GPT-4 strongest point, I have noticed the same degradation in quality.
And as I know there will be many commenters asking, here's my experience.
Four months ago I released a mobile app that wraps the "Open"AI API and allows a more private use. The app also includes 15 domains with over 150+ editable prompts, specifically crafted to help users get the most out of GPT.
I initially crafted these prompts in English but given I wanted to allow also non-English speakers to make use of them, I started to translate them in Italian and German.
I wrote a small script that took each English prompt and, with some more prompt-fu, translated them to these languages, using GPT-4.
As I'm fairly fluent in both Italian and German, I was able to verify the quality of these translations.
Well, around end of May, when I first noticed some weird answers from GPT, I ran my script again and (surprise!) the quality of the translations is visible inferior.
On a different note, I noticed that from one day to the other, any prompt would get an empty reply in the app, only to discover that "Open"AI has also made a subtle change in the json format of the API response that made broke the parser in the app.
Admittedly, 150 phrases is not a huge sample size and I could/should have used the default json parser.
I don't trust "Open"AI and will, as soon as it's feasible, change to a different model.