You cant injure 300 Rogues if you can only access 20 and that is the point. For me a lot of fighting was 35 battles. This left me with 20 injured rogues.
Well, according to stats, between Apr. 4 and Apr.7 your won battle count went up by 104. Now, stats doesn't update in anything approaching real time, so it is impossible to know when those 104 battles occurred over those 3 days. Also impossible to know if you lost or surrendered any. But it is certainly plausible to me that they happened within a somewhat short period of time. Maybe fighting just before and just after GBG reset?
In 104 battles, or more if you lost or surrendered, 300 wounded rogues is plausible, given their slow heal time.
Or maybe you just didn't scroll left far enough to see the healthy rogues? Healthy ones are leftmost. You would not be the first to make that mistake.
Or maybe it's a bug and Inno is only showing you injured Rogues when you have healthy ones. But this is a game mechanic that has been in place and unchanged for years. If it was a common issue, there would be more than just you complaining about it here. I suspect it's not a bug, these things almost never are, but it's certainly possible. Document it then report it if it happens again.