I found that the consoleText stops updating once a build command's output reaches 5000 lines. It doesn't update until the end of the build job, and then the rest of the lines are updated in consoleText. The consoleFull continues to update as expected, beyond the 5000 lines, even as the consoleText is not being updated.
I have a client process which monitors the output of consoleText for changes on a build job. It stops updating at 5000 lines, then when the job completes, the rest of the build output can be found in consoleText. This gives the appearance of a stalled build job.