KQL or Lucene with RegEx

Hello all! I have a log file entry that I am able to find, just not using the search criteria I'd like. To start, here is an example of a log file entry:

[2024-09-06 13:01:12.587] DevTecmNode01-devTECMBatchCapture1 /task-scheduler-4 ERROR com.thrivent.ecm.ecapture.exception.ECaptureExceptionHandler - error $211$ **#y#3#2#**nested exception is [ inputs=M NON FINANCIAL, errorType=[errorId=E14businessException=false], additionalMessage=null ] [com.thrivent.ecm.ecapture.exception.ECaptureException: Invalid Document Sub Type 2 Code.###nested exception is [ inputs=M NON FINANCIAL, errorType=[errorId=E14businessException=false], additionalMessage=null ] [com.thrivent.ecm.ecapture.exception.ECaptureException: Invalid Document Sub Type 2 Code.

Or, if you'd care, you can simplify what that log entry looks like down to this string:
...error $211$ **#y#3#2#**nested exception is [ input...

The rules this follows is that there is one character between those # symbols. And there are one to many before and after it. So to me, this would be what we are searching for:
.*#.#.#.#.*

Where .* is one or many characters and the periods in between are just one character long.

If I search for that exact string, it does find the above row:

AND message: "#y#3#2#"

But what I cannot seem to do is get this be a regular expression.
I've tried these in my Lucene query so far:
AND message: /#.{1}#.{1}#.{1}#/
AND message: /#.#.#.#/
AND message: /.#.#.#.#./

None of those seem to match and return the one log example above. Can anyone help me out in getting a regular expression search to work, looking for four # symbols with stuff between?