Output is wrong for processes that update stdout in-place using '\r', etc
Love this tool!
There are command-line tools (example: "npm install" for nodejs, but there are tons of others) that use '\r' character or similar techniques to re-write over the current line. Looks like these aren't showing in your tool at all.
For a tool like yours, the best thing to do might be to rewrite your "tail" with a pre-step that does something like "tr '\r' '\n'" and turn those into real CRs so we at least see when the output changes, if it isn't in place. For example, that's what CI tools like CircleCI do.