Claim denied after 6 weeks - they say 'not covered' but won't explain why

So my homeowners claim for water damage got denied last week and i honestly don't know what to do. Filed it back in February after a pipe burst in the wall behind our bathroom. The adjuster came out, walked around for maybe 20 minutes, and then i didn't hear anything for 6 weeks.

Finally got a letter saying it was denied due to "exclusion 4.7 - gradual damage." But here's the thing - this wasn't gradual at all. The pipe literally burst during a cold snap we had. There was water everywhere in like an hour. I have photos and my plumber confirmed it was a sudden failure, not a slow leak that went unnoticed.

Has anyone dealt with this kind of blanket denial before? Do i actually have a shot at appealing this, or am i just going to waste more time and energy?