Upgraded from 11.6 to 12.x and now getting an error

On a local lab F5, I created the simple rule below:

ltm rule testing_URI_path {
when RULE_INIT {
    set test_uri "/path/to/file.ext?param=value"
    log local0. "\[URI::path $test_uri\]: [URI::path $test_uri 1 1]"
}
}

Which resulted in the log output below:

Feb 19 17:49:40 bigip1 warning mcpd[6521]: 01071859:4: Warning generated : /Common/testing_URI_path:3: warning: [The following errors were not caught before. Please correct the script in order to avoid future disruption. "end value (2) not greater than start value (2)"109 23][URI::path $test_uri 2 2]
Feb 19 17:49:40 bigip1 info tmm1[25355]: Rule /Common/testing_URI_path : [URI::path /path/to/file.ext?param=value]: /to/
Feb 19 17:49:40 bigip1 info tmm[25355]: Rule /Common/testing_URI_path : [URI::path /path/to/file.ext?param=value]: /to/

It looks to me like the form of URI::path with same start and finish values is set to be deprecated in a future release, and while the parser is allowing it now, it's warning about this usage.

You might consider calling F5 support to verify if that's the case.