When an error escaping in JIRA JQL is made the following error comes up:

Error in the JQL Query: '\$' is an illegal JQL escape sequence. The valid escape sequences are \', \", \t, \n, \r,
, '\ ' and \uXXXX. (line 1, character 16)

The \uXXXX refers to escaping JAVA source, however, it's been found that this does not work.

There are multiple examples of this, but let's take the special character "\".

I can create an issue with the summary:

foo\

Then do a search for it using the JAVA sauce:

summary ~ "foo\u005C"

JIRA will return the following error:

Unable to parse the text 'foo\' for field 'summary'.

This only seems to happen when the special character is at the end of the line.