Unfortunately, while your reproduction produces the same issue that I am experiencing, it is not the same cause. I have triple checked my JSON syntax, and have confirmed that just replacing {{myMultiSelect.value}} with [] produces value JSON with no errors.
On a possibly unrelated note, I have just noticed that when setting the value of a multiselect option, I am getting an error saying that I provided an arrray when it's clearly a string:
Perhaps this is a root cause?
I found this thread which shows the same issue, saying that the default value field is the problem:
My default value looks like this:
Edit
Ok so I have discovered another issue that seems to be causing the problem. In my query I have the following:
This gives an error.
If I change the $in to this:
the error is resolved.
However, if I instead remove the $gte to make it this:
it also resolves the error.
So, somehow removing either of these parts of the query resolves the issue. I can't understand this, but maybe you will.