PageSpeedInsight Main Thread delay

I'm having some questions on PageSpeed Insight. When I'm doing perfs tests on LightHouse and WebPageTest, I'm getting really good results but on PageSpeed, I've got a strange results (I get 35/100 on desktop VS 93/100 in Chrome dev tool's LightHouse). The main difference is this line :

Minimize main thread work Other 29 800 ms

Does anyone knows what's happening in "Other" ??? And why does it takes near 30secs ???

I'm not very stressed about the pageSpeed note but I'd like to understand what's happening behind this 30secs....

It happens on multiple website...

You can find an example here : https://developers.google.com/speed/pagespeed/insights/?hl=fr&url=https%3A%2F%2Fwww.extralagence.com%2F&tab=desktop

Thanks a lot !