@Lodan,
Here's my tuppence worth!
1) Always know your background before deciding how to tackle for example.
A) boardwork can be 1 coated or 2 mixes from same gear if done properly!
B) High suction can be 2 coats from same gear.
C) Painted substrate always best to let 1st really pull in and use a fresh 2nd mix
D) Artex 1 coat of magic mix followed by a normal skim 2nd coat.
You can't always take short cuts but the secret is to use them where you can.
Also as everyone will tell you any wall REGARDLESS oh how applied will look shite with any acute light angle down it!!!
I will stake my home on the wall in question being a paint surface which you didn't allow the PVA to 100% dry also probably a week ratio before then trying to use 2 coats from 1 mix hence it sliding and smudging as it stiffened up!
If ever using 2 coats from 1 mix or 1 coating ALWAYS ALWAYS let pva go totally dry even if you have to return following day etc.
And remember depth is skims nemasis often best to dub out heavy Areas first if needed ie beads etc.
Good luck pal