It is likely to be something that happened in the last month and a bit, we don’t deploy our hosted enterprise customers as aggressively as we deploy this site (which is deployed every commit).
There have been some changes that could have caused this, @joffreyjaffeux will report back in the next day or so.
As to forking or patching to get compatibility, this is not an easy task. Discourse is a pretty rich application and we tend to take advantages on modern browser facilities, this is a moving target. We do not like complicating our internal code to work around browser spec deficiencies, we only do so when we have no choice.
That said, we are pretty committed to have a readonly view for crawlers, so for example:
Which will work on almost all browsers even ancient ones.
Let’s wait on what @joffreyjaffeux has to say here.
If you somehow want to fallback to “readonly” view for browsers that are not supported (instead of sorry, browser is not supported) this is work I would not mind exploring, shoot us off a separate message here to