Created Jolla account. Even with access to store repo, couldn't downgrade the two packages - not found. So, I tried zypper refresh & update again, and this time, I included the 12 packages (including libhybris) were previously held back by conflict with gcc-5.2. This time, when I tried to reboot after upgrade, Fxtec Pro got stuck on splashscreen. Beautiful but entirely unhelpful. The only idea I have now is to attempt to flash the device again, as I did after accidentally formatting system partitions.

Thank you. Best wishes.
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Per aspera ad astra...