osmo-bts sends invalid/no SI message at TC=0 if SYSTEM INFORMATION 1 doesn't exist
SI1 is only required if frequency hopping is used or if NCH is used. So it's optional.
If OsmoBTS has no SI1 configured, it will transmit the empty SI1 buffer at TC=0, and as a result no valid SI will be broadcast at TC=0.
This is why the various BTS_Tests.TC_si_sched* are currently failing.