Hi,
just want to put my mustard in ... I know it is an older thread ...
I had the same issue with "waiting (TTFB)" as shown above at products page ... Card page and payment page.
In my case it was an issue with file system security rights.
I used Linux command:
chmod 777 -R *
At the root folder of my shop and the issue was gone.
To be clear, in my case it was an Testserver ... not productiv.
Do not do this command on your live Server, because it can cause security issues.