I believe the problem here is that the alert does not exist at the time the log file is created / parsed.
Directory Monitors have a limitation in that they do not persist filters (or alerts) when saved as part of a workspace. The latest beta version of LogViewPlus introduces the concept of a 'directory manifest' which addresses this issue. This feature is still under development, but I can post back here when it is ready for release.
Note that directory manifests require the file name to be known in advance. It is not currently possible to alert when a new, previously unknown file is created. For example, this not be possible for file names with date patterns.
Hope that helps,