There'll be lots of experience along shortly to reply, so here's my take, based only on experience as a student, some time ago, and as a glider instructor at some stage. When I morphed into power flying, I had three for the mostpart, which would have been too many were I a complete novice. What I got though, if I attempted to use any of it as an excuse, was a dose of 'By now, you have enough gliding experience to cope with x or y' and of course, they were right.
It depends where you are in your training. In the early stages, you need continuity, I think, when perhaps alternating between two instructors is the most you could cope with. You very quickly learn one thing not on the syllabus: each instructor has his/her own style. Later on, when you are more comfortable with things, a change of instructor will not phase you and can be useful, adding new angles and opinions. The benefits can balance the perceived disadvantage of lack of familiarity.
It would seem from your post, though, that you are uncomfortable now and if you have already had to mention it, you know the answer. If you do a search, you will find that this subject has come up before and IIRC, most will agree that a quiet word with the CFI should work.
If the school is struggling to keep the wannabes in work in difficult times, it makes things harder for everyone, but a student is owed a certain amount of continuity. Six in eight lessons is too many (sounds like my early days in gliders) and more likely to deter an early student than encourage. Don't feel bad about speaking up; it may be no one has realised until you do so.
Good luck.