I had the same question once, and licensing team told me that I'll have to upgrade my PLM from 10.5 to 11.5, and it is not enough to install the license definition files (don't know if I believed them, heh).
Anyway, once you upgrade to 11.5 you can place 10.x and 11.x licenses on it. Also, 10.x licenses are valid also for 11.x clusters, so you won't have any issues. I would recommend to upgrade anyway.
BTW, all the above I did myself and it is all working fine.
And... if you're using HCM-F server (if you're on HCS deployment like me) you'll also have to upgrade this server, too.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...