Yup, the same situation: It's there on LTS but not on nightly. Also nonexistent functionality on frr, so it can go from the completions too. (Although the CLI files are still in the vyatta-op-quagga repo.)
However it still seems to be stuck in reset on nightly:

$ reset ip bgp foo rsclient
% Unknown command:  clear ip bgp foo rsclient

Viacheslav seems to have migrated a good portion of Quagga show commands to the XML template format a while ago and the remaining completion file for ip bgp scan also got deleted then. I can see that the useless command completion for it is still there on 1.2.5 LTS but it's gone from the nightly builds.

Could not reproduce this on a clean install. That error is printed iff the IPsec process is not running, obviously enough. When I set up IPsec and ran the command, it simply printed out the table. Maybe there was a hiccup with the nightly build you used if that error happened with a running IPsec process.

This command was removed from Quagga five years ago and never made it to FRR.