The system keeps you in probation as long as you get negative reports that are deemed to be accurate.
The threshold isn't that you have to be honorable to regain your honor, the threshold is that you have to NOT be dishonorable. I know it sounds like I'm splitting hairs but it's not.
This is based on two riot posts within the last few weeks about honor:
{quoted}
Went ahead and checked your account, and it seems you're definitely doing a much better job since your Honor dropped back in September!
I'm still seeing a few cases where your chat's a little abrasive, and that is slowing you down. Fortunately though, your Honor is now unlocked and is progressing at a steady rate. Work to keep your behavior as positive as you can and cooperate with your team, and you should soon see your Honor grow. :)
and
{quoted}
So basically, your honor progress hasn't been going up as fast as it did before due to some borderline dishonorable behavior. Your loot will unlock once it's been shown that you're honorable again, but there are some chat logs that showed borderline punishable behavior. If you want more context on exactly what happened, feel free to hit up the player behavior agents in a ticket.
Being honorable means when you get honor, it helps you go up honor tiers.
Not being dishonorable means that you don't get negative reports that are accurate and true. If someone reports you for negative player behavior, that halts your reformation progress. This means if you are harassing someone mildly but still get honored in that game but someone reports you for negative attitude or harassment and the IFS deems your chat to be negative and harassing but not bad enough to warrant another punishment, you're going to get your honor gain halted and thus you will extend your reformation period and not be eligible for rewards.
EDIT: if you've had issues with chat restrictions, you should use this test... are you typing because you're upset, annoyed, disappointed, or angry at someone? If yes, don't hit enter. Just focus on your game and keep on truckin'