1) the issue with 'empty database' is confirmed. It is related to 'autocomplete'. 'drop database' and 'truncate database' are not affected.
We will release 5.21 beta1 with a fix for this in a few days.
2) However we cannot reproduce the slow import.
Can you tell what 'Remote connection' means? HTTP??
If so that could depend on the server load then.
Can you reproduce with both versions installed at the same time?
(import with 5.19 … measure time .. drop database .. measure time)