Spotted this while walking out for supper after a day at the CNC Workshop:

Then it got worse:

The lower left block remained fixed throughout the glitzy scrolling / rolling / blinking updates in the sign’s repertoire:

The affected block is 64 pixels tall and, at a guess, 128 pixels wide. Looks like a module enable failure…
Some of those modules are driven serially and daisy-chained, so a single break in the data chain could also cause this behaviour.
Aye, and in that case, it’s always the connector!
A few days later it was OK (at least on one side), so either a repair crew levitated up there or the mice moved out…
Could be weather related.
Bad connector, exposed traces, or anything that doesn’t like water and then wind, rain, and some bad seal. A day or two with a couple hours of sunshine would also “fix” it again.
Don’t blame rodents if you can blame an engineer…