Never heard of a Navigation Progress Check in the twelve years that I have been flying.
As it isn't a requirement in the actual syllabus, it might be a school specific check where they have you fly with another instructor or maybe the chief flying instructor to assess your progress on the course, this being a navigation progress check.
These are to ensure you are progressing well and are on-track to skills test standards.
These type of in-house checks are quite common in the USA when on Part 141 courses, for example the FAA IR Part 141 when using the Jepessen Syllabus requires three stage checks to check individual progress throughout the course.
This also ensures all instructors within a school are teaching their students standardised practices for that school.
I wouldn't worry about the check, sounds as though it is an in-house flight check. The instructor that you fly with may carry out a dummy navigation portion of the skills test, i.e. you plan to fly a route. Once you identify your first waypoint they will get you to divert to a specific place, so in flight re-planning is required. Thereafter they may get you lost and you have to find your whereabouts on a chart. Be warned with this bit... they may spin the Direction Indicator on you... always check the DI against the compass!!!
Anyway all the best but I really wouldn't worry about it. Enjoy it and treat it as another instructional flight...