you seem a bit defensive of wordpress
Only based on experience - honestly. FWIW, I've also logged/reported bugs and tried to bring in core devs to look at potential WP issues. Only a couple of days ago, I was pinging a plugin dev because we suddenly got multiple reports of exactly the same problem after they upgraded a specific plugin.
At the end of the day, it's going to be all based on numbers. If we have 30 people are having the same problem on different sites/servers at the same time right after an upgrade, then there's every chance that there is a bug. But if it's just one site here or there, then 99.99% of the time, it's site specific.
Upgrades are not always 100% successful. They can mess up for a variety of reasons - such as a drop in communication during the transfer process or a plugin or theme blocking part of the upgrade process. If there is a core bug, it will hit thousands - if not millions - of sites. Not just one or two. If it's an upgrade hiccup, only a few sites will be affected.
All of my comments and suggestions thus far have been based upon what you have reported, what I can see in your page's source code and my past experience in assisting with these issues. Given that you were becoming very frustrated in the previous topic with the lack of response, I have been doing my best to assist you. But if you would prefer that I stopped doing so, I will do as you ask.
Best of luck, I hope you do find a solution to your issue. :-)