As I said I have unlocked galaxy s9 + i took my tmobile sim card and inserted a different carrier sim card and I manually checked for updates there was 2 updates the latest one was the April security patch!
This worked for me too. Using an ATT sim card I was able to update my phone to the April security patch. Before that I was on the january patch with my carrier (T-Mobile).
As an update to my original post: after chatting with Samsung tech support and them sending me to a local Samsung service center, (ubreakifix) who tried unsuccessfully to use some kind of "fancy" factory data restore, I ended up with a phone I had to reinstall everything on and yet I was still at the January security update--plus they said, it must be your motherboard then and we'll have to replace it. I called TMobile and their Tech support rep assured me, "after talking to other reps" that it must be a problem with Samsung and that there was nothing they could do and that they had never even heard of the problem. So, eventually, after waiting months with no update from January 1 on T-Mobile, I got a sprint sim and put it in. Within seconds, it found the latest upgrade and is updating my phone to the June Security update as I type. Yay! Though, what the heck, Tmobile?! How come every other carrier can make these updates available to unlocked S9 phones and you can't. Not only that, you can't get off your behinds to be honest with your loyal customers and help them out.
Yes like others in the forum the only way to push out the updates is to take out your sim card and put in a different sim card and viola 2 security updates were pushed out. all caugh up July security update. With my case i have T Mobile and removed the sim and inserted my International sim card Vodaphone that i use when traveling to Europe. I am sure any other sim cards will work. Please note that i tried previuosly with a card that was unprovisioned and it did not work. I had to use an active sim card from my other carrier hope this helps