CK are not real scores.
Unless you get your true FICO scores nobody can really offer advice on why.
CK is not real scores is inaccurate. They are not FICO scores, but they are real scores.(Vantage scores) The op is aware of that and they already acknowledged that several times.
Also saying “nobody can offer advice unless he has real FICO scores” is also inaccurate.
I’ll take these one at a time.
Your score did not go up when the collection was removed because you still have another collection. You have already taken the score hit, and it will not recover until the last collection is removed/aged off etc. The scoring model puts more weight on the final collection. You can remove 5-6 collections and see very little movement and you remove the last one and your score jumps up. That’s just the way it works, nothing you can do expect try a PFD on the last one.
New credit can lower your score because it reduces the average age of your accounts, which is also a factor in your score. Between the hard inquiry and lowering of your AA you are going to take a hit. Your score will recover when your youngest account ages a bit.
How are you determining your average age of accounts? If you're using CKs summary page, it only includes open accounts, which paints an inaccurate picture.
OP, I highly recommend you stop using CK for anything other than your weekly TU/EQ reports immediately. Their scores, summary pages for your different credit components, etc. are completely useless.
Your FICO scores will not increase much if at all with the removal of a collection if you still have another major negative item present on your CR.
Credit Karma is a joke. They are good on providing you FREE advice on what you're file looks like but they arent good at all with getting you a real FICO Score. Vantage Score3.0 is what the use, and maybe that model does not give points for collections, BUT Fico Score 8 which is used by many lenders including current credit card companies probably gave you some points back.
There is nothing I can do since I do not understand Vantage Score 3.0
As I said in my previous post, anything on the CK summary page should be ignored. Pretend it doesn't exist.
You can get a free EX FICO 8 score at creditscore.com or creditscorecard.com. You can also do a dollar trial membership at CCT/Experian and get multiple FICO scores, I think 9 at last check.
Obtaining your own credit scores never hurts your credit in any way, I'm not sure where that perception ever came from or why commercials constantly say, "checking won't hurt your credit" because checking your own credit never hurts your credit.