My build is marked successful however I have 1 critical failure.

Here are the values from the robot plugin table on the build page. As you can see this table makes no sense. The % critical passed is not accurate.

Robot Test Summary:
Total Failed Passed Pass %
Critical tests 2458 1 2457 100.0
All tests 2838 259 2579 90.9

The actual pass % is 99.959

Opening the report.html, it's red as expected and lists the single critical failure.

My thresholds in the Jenkins job configuration is the default (90.0% for unstable, 100.0% for successful). I suspect there might be a rounding issue somewhere.