Greetings CMDR o7
I've been in the same situation recently. My first piece of advice - be patient
EDDB/EDSM/INARA can't guarantee that the faction you looking at actually belongs to the players or not.
I requested several times and ended up coding a script that parses EDSM dump with habitable systems to find a specific one.
It's not a very fast process. Some factions can expand to this system at the moment you requested, and it blocks spawn for a new faction. Some systems can have 7+ factions - this is also blocking. Some specific states (can't say for sure) can be blocking as well. Even if the submission form shows "

" sign - it still not guarantee that system will be suitable.
First of all, I'd recommend filter out all systems with 7 or more factions. It will increase the chance. Even if requirements say it needs to be 7 or less - when 7 factions present - some 8th faction can expand to this system.
Second - visit the target system on your own. (Maybe with ED Market Connector enabled - it will update inara/eddb/edsm).
If it's not a very active system - you might notice that the system info was outdated on the web, and you only can see fresh data in-game when you visit it.
PS: What systems was that?