Using Conan in the build pipeline, it can produce lines to the output like:

"foobar/cci.20200101: Appending PATH environment variable: /Users/johndoe/.conan/data/foobar/cci.20200101///package/hash/bin"

These lines are picked up by Qt Creator's build output parser as errors (they are rows in the list of Issues tab) but they are just regular lines.

By using Tools/Parse Build Output and the string above, the problem is reproducible on macOS.

Interestingly, we couldn't repro it on Windows. Also interestingly, putting ":" at the beginning of the line makes the error disappear, suggesting that it's some sort of a regex problem.