US 05 fermentation question

[Clint]

Hello all,
last Saturday I brewed the GH dry stout and used US 05.
It was left to get to pitch temp,lid on and blow off tube fitted until Sunday morning as I couldn't chill lower than around 30.
By Sunday tea time there was activity and it bubbled steadily all week with only a very little bit of krausen through the tube. This was the same last night before I went to work.
Getting up a short while ago I've checked on it and it seems overnight there's been another massive krausen as the fv headspace is full and the blow off bottle has gone brown and there's a deposit of yeast in there and loads of foam...
I've never seen a delay like this before...

 

[MyQul]

I havent had anything quite that dramatic but I've had more than one brew throw a second krausen several days later

 

[Linalmeemow]

I always find stouts take longer to properly get going but that's quite extreme - does it smell and taste OK?

 

[Clint]

Smell fine coming out the blow off tube..not tasted it I'll leave the lid on for now..