It's unfortunate that some equipment providers do not thoroughly test their products.
We buy them assuming that they are well wrung out, but in reality, many test only enough to get the certification, and many TSOs leave environmental test requirements up to the end user to specify or confirm.
It is amusing for me to look at the DO-160 test categories for many certified products that we install on our planes. Many are filled with "X"s indicating that no testing was performed or claimed in those areas. I've see altitude encoders that basically only tested for temperature. Everything else is X's.
Here are the test categories for the ACK E-04.
Notice what I highlighted. No testing for radiated or conducted susceptibility. So, let's say you have a nice high powered ATC surveillance radar on the field that is sweeping your plane every few seconds. You have no evidence that the unit will not respond in a bad way to that. None. (the aluminum foil wrap was not a bad idea!)
Environmental qualification testing is expensive. Figure $100-250k or so for a basic series of tests, if they all pass the first time. (and every time you make a design change, you have to run though an analysis to determine which tests have to be re-run.)
Oh, and I highly doubt these occurrences are due to single-event or multiple-bit upsets (SEU MBU) from cosmic rays. Those affect memory devices (flash mostly) and i doubt the ACK is using a flash based FPGA. Even those typically have mitigation features. (that's another analysis!)
Take a look at the DO-160 environmental qualification test form on the next piece of avionics you are considering. It might be enlightening.
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