Ran ./run.sh build v0.20.6 with SIAB and it shows the following. I don't know what does cache means below. I am a Docker n00b!

Step 9/13 : RUN cd ~ && git clone https://github.com/steemit/steem.git && cd steem && git checkout ${steemd_version} && git submodule update --init --recursive && cd ~/steem && cmake -DCMAKE_BUILD_TYPE=Release . -DLOW_MEMORY_NODE=ON -DCLEAR_VOTES=ON -DSTEEM_STATIC_BUILD=${STEEM_STATIC_BUILD} -DSKIP_BY_TX_ID=ON && make -j$(nproc) && make install && rm -rf ~/steem
---> Using cache

I tried with the exact above options and ran the build again and not able to reproduce again. I think there is some cache or left overs from Docker.

Why don't you delete the docker folders and also do apt purge docker and try again ?