Pre-Script: In the past, I have been doing this on a person by person basis, but I figured a blanket message would serve just as well, especially for those I cannot get a hold of.
If you were in the clan at one point, and you come back to find you are not, you have most likely been removed from the clan to make space. This does not mean you have lost your spot in the clan if you so wish to have it, just that you have been inactive and we have needed the space. This also does not mean that you have been removed from GOTR, your character has been removed to make space. Nothing more, and nothing less.
If you would like to rejoin the clan (or if you haven't yet joined the clan but would like to, for any newer players reading this) simply state either on the invites forum post, or preferably in the discord #warframe channel about wishing to rejoin. Be sure to include your In Game Name (IGN) so that I can add you as well.
Sorry for the inconvenience, as I know it can be disheartening to come back and not have the clan.
If you are wondering why we do this instead of simply expanding the dojo to the next tier (which is technically an option) it is because the research costs increase drastically with each tier, (ie: Hema research goes from requiring 15,000 mutagen samples to requiring 50,000 mutagen samples, not even including other resources required, or other research projects to do) and without an active base of players to support that increase, it prevents the active players from getting the research benefits.
Don't be worried about being removed from inactivity either (though I will admit, activity is nice, it is not a requirement) I will not remove people who have been inactive for less than a few weeks (at least, we have many people in the hundreds-of-days range to go through first), and if we ever have an active enough player base for that to become a problem (albeit a very good one to have), the dojo will be taken to the next tier, as we would be able to support the increase then. And like I said, if you are removed, and wish to rejoin, simply state your wish, alongside your IGN, and you will be added to the clan as if nothing had happened.
If you have managed to read through all of this, thankyou for your time. I look forward to seeing all of you in the Clan Ops, if you can make it, or at least in the discord or the forums.