There was apparently a nice bug well hidden in linuxrc, that was recently
fixed:

https://github.com/openSUSE/linuxrc/commit/b51ff997fee906777d4cde23ddbc0d3afd242df6

It has the very negative side effect on Tumbleweed though that any downloaded
NET installer is now only valid until the FTP tree is updated to a new
snapshot: something that makes Tumleweed Net installers very impracticable, as
the same disk can't be used for very long.

This was first observed and caught by openQA:
https://openqa.opensuse.org/tests/227377#step/welcome/7: this test uses the
LATEST TW snapshot NET installer (to be tested, not yet published) and installs
the 'previous' (currently published TW snapshot).

This entire check feels like we need something more suitable for Tumbleweed,
ensuring to not make the NET installer incompatible every day with what is
published