While tuning my setup I noticed what appears to be a bug with merging events. Whirlwind with a Fury Warrior hits 3 times with each weapon for a total of 6 hits. If I set my Max Interval to 0.3 from Last Event I'll always see a proper event with all 6 hits merged. However, if I set the interval to 0.25 or 0.20 I start seeing events with only 4 hits merged. I don't see a separate 2 hit event, the missing 2 hits simply disappear into the ether. If I set the interval to 0.15 or 0.10 I start seeing 2x events or no events at all.

I see the same issue when I start going below 0.4 from First Event as well.

It's easy to repro this by spamming Whirlwind on a target dummy.

Here are my merge options

As fury dw 2h and interval even at lowest possible value of 0.01 and the rest of the settings same as yours, I see 3 times "damage x2" on a single training dummy. Can you please attach your "World of Warcraft_retail_\WTF\Account<accountId>\SavedVariables\ClassicFCT.lua"? Also which version of the addon are you using? Thanks for taking the time to report your issue.

I found my issue. I had "Hide Below Absolute Threshold" enabled to filter out Siphon Essence spam. Since Whirlwind hits like a limp noodle it was getting filtered out when it wasn't merged. Sorry for the false alarm.

I guess a follow-up request would be to filter specific spells. Is that something you'd be particularly interested in?