[SDK 1.5.4 has no voice]
This might be related to commit c77c2a6aa13accbc558888ab788d1148eb9aeb1a in osmobts - see https://projects.osmocom.org/issues/1661
osmo-bts has no commit c77c2a6aa13accbc558888ab788d1148eb9aeb1a. ...you mean libosmo-abis.
If you roll-back this commit, does voice re-appear?
Wow, it actually does! I was pretty sure this would not fix anything. I have discussed in detail in OS#1661, and see https://gerrit.osmocom.org/1011 .
A pressing issue which you seemingly ignored is that your osmo-bts commit 654175f33bd412671e3ef8cdd65c0689d10f278c breaks voice on SysmoBTS. Could you grab a sysmoBTS and verify+fix it soon? Otherwise revert.
~Neels