tlmgr update --self fails on 2019-04-07

[Karl Berry]

    > To repair your TeX Live installation download and run:
    > http://mirror.ctan.org/systems/texlive/tlnet/update-tlmgr-latest.exe

For the record: I gather you are working with the pretest (thanks), so
downloading .exe from mirror.ctan.org will not work out. Have to
download the update-tlmgr-latest.exe from pretest repo.

Sorry, I have no clue about the real problems you're reporting ...
--thanks, karl.