Thank you for your response.
Yes. Although I get the error the post still saves. Yes after increasing the PHP memory I did restart.
Storage info says:
Total cached CSS/JS files: 187898, 504.99 MB
It’s a very large site approx 10,000+ pages but I did not realize that the total cache was 504.99 MB so 512M PHP mem may not be enough. I will try doubling it.