I can't comment on HTML files, but I would have thought that the shield was just a communications device and and the size of the file would be immaterial.
The deafening silence in response to your plea
Anybody else experiencing the same problem?
Is likely to mean "no". This means you need to ascertain why you have a problem that nobody else has, particularly as it is very likely that more people use generic than official shields.
It could be that the shield is suss but, if so, it is probably just that one.
It could be that you are the first person in the universe to tax it with a large HTML file, but it isn't likely, and you don't say what large is anyway.
But the absence of any response suggests that user error is the most likely cause of your problem. This is not to deny that you have fixed a perceived problem, but you might not have fixed the real one.