Comment 1 for bug 1881532

It looks like the focal version of named is compiled with lmdb support where as the bionic version is not. Hence the change in behaviour:

# lsb_release -c; named -V | grep -ohE 'with-lmdb|without-lmdb'
Codename: bionic
without-lmdb
# lsb_release -c; named -V | grep -ohE 'with-lmdb|without-lmdb'
Codename: focal
with-lmdb