The workaround would be to remove packages, which you don’t need as they are not critical to function e.g. routing.
HBK is a development branch as you can see here https://docs.turris.cz/geek/testing/ and some occasional bugs might appear.
It was caused by a recent Python3 update in OpenWrt 19.07. We reported this issue to upstream https://github.com/openwrt/packages/issues/12680 and there isn’t a solution so far, yet.
For this reason, we decided to freeze packages feed before Python3 update for Turris OS 5.0.3 (currently in HBK) and the packages are already there except Turris 1.x routers (build should be ready in within hour). Also, HBL builds are running. Should be solved within a few hours.
There was also a possibility to revert that update as quick&dirty workaround.