This might be a device limitation; I can reflash TWRP fine on my RN10P running crDroid 9. (and it holds after reboots) NOTE: crDroid 9 on RN10P sweet has an optional crD9 recovery download, whereas RN11 spes does not.
There were app crash and system error issues which necessitated using the crD9 recovery to install on the RN10P.
I have to wait a few more days in order to test on the RN11.
It´s all about software, not a device limitation precisely, they´re different devices, so the builds may be different though. Some developers can make a TWRP to have a way to be auto-injected, and can revive through reboots.
Some ROMs can need of the same recovery that is built by the same community, just because that community want to put it this way, all relies in that, otherwise, if a developer want it, no sense to need only (in this case) of Cr recovery, because any custom recovery can do many more than it, TWRP, and Orange Fox recoveries, just to mention two, are many more enriched.