After take off with Flaps 2 at about 500 ft above ground, the airplane suddenly pitches up to about 40° pitch up. Countering that with stick full forward doesn't work. After a few seconds, the aircraft starts responding to stick inputs again.

This only happens in MSFS 2020, I have never seen such behavior in MSFS 2024.

A35K. Exactly the same occurred to me. Pitched up, yet uncontrollable and then crashed. Have uploaded to latest SU4. WASM files deleted etc and the 350 is a mess. Multiple load up issues where screens not showing correct data and twice scrubbed flights due to ‘red screens of death.’
 

Had occasional WASM crashes, although now much worse since update. This is beyond a poor substandard product inibuilds even though purchased at lower cost. 

Not only flap 2. it happens during all takeoff phase....

If you engage the AP when nose pitching up, it will be happened again when you disengage the AP.

Has happened to me only in Flaps 2 or 3 config (dont ask why i was in a flaps 3 config takeoff ;))

First time I thought nothing of it, but second time I noticed it.

This happened to me on a go around the other day, not sure if it’s a one off weird thing. I’ve taken off on flaps 2 before without this issue though