This has to be an issue on Jolla’s side there is no other explanation:
Ubuntu 20.04 LTS
Latest SDK (offline or online doesn’t matter)
Latest virtualbox
Run the SDK, select 4.2.0.24 armv7hl as one of the architectures (for me it was the only one). You will get repeated “Hash error this is temporary please try again later” after the tool is installed, at around 17% completion.
indeed there is an issue: Somehow the file has been truncated on the server. Looking at the timestamp it seems this has happened when we published SDK 3.7 to all users. Thanks for the reports, we will fix this asap.
P.S. I’ll mote this post to the more appropriate “Bug Reports” category.
Now the package has been re-uploaded to the server. Please note that it might still take a while before the change has propagated to all caches, so if you still get the error, try again after a while.