Well in the event that someone else stumbles upon my question, here’s the answer:
When compiling for HTML5, the same rules apply that would if compiling to Mobile platforms. The issue here is that the material that was unable to load was created from over 5 texture samples, which is above the limit that UE4 supports for mobile. You can read more on material limitations on Mobile here
Thanks for the help. I had a similar problem. I didn’t know about all these limitations until i noticed some characters were not in my html version of my game but they were in the pc version. Thanks.