T5HO and T8HO ... But T12HO?
(I'm in California -- and T12s have been banned hereabouts for years and years.)
My first impulse is to say that the ballast is a mismatch. (I'd junk the T12s and move to T8s.)
BTW, shorting neutral conductors on the frame is a classic cheat for systems that have too much impedence on the neutral.
I'm forced to presume that said short was accidental. If it was a hot -- I'd wonder about the C/B and the grounding/bonding conductor.
Lastly, always swap out the tubes for a known sweet set before tearing your hair out.
A system with a 'casual' short may also have issues in its tombstones. (This issue is much, much, stronger with exterior signage. The conductors are dinky and the contact surfaces are minute. They may permit a start surge to pass -- and then fail to sustain normal operation.)