All 3 test clocks need to be in the same "domain" in order for them to be allowed on the same scan chain. RC has the concept of "clocks" and "clock_domains" for both functional and test clocks
You can either ensure that you define all test clocks to be included in the same domain (use the define_dft test_clock -domain switch), or apply this command to put all test clocks in the same domain:
Use -h to see the full usage of this command.
I hope this helps!