> This was with the default settings after flashing Crimson

This is strange. See this post concerning the battery life: https://puri.sm/posts/librem-5-battery-life-improved-by-100/. Have you updated the modem firmware?

You are right, I have case 1). It is quite likely that Byzantium is (was) much less stable, as it required a lot of hacks and relied on a very old Debian version.