Let me get this right: Each month you send invites to 70 different people. OK. How do you get to 1177 people then? January to May are 5 months. 5x 70 isn't anywhere near 1177...

Sorry, Holch, I don't know how I got to the number 70...

Over the 4 months we sent 1,177 invitations. Each invitation is, naturally, to a unique token.

This averages to around 300 invitations per month. Or to be more accurate:
January - 250
February - 300
March - 313
April - 314

We are already in mid-May, so it will not take long to see if anything changes.

It's an interesting case. I also would be wondering what is going on. But of course we would expect some differences over the 4 months. So I think it is good to keep an eye on this. Keep us updated on how it is going. We already have excluded that Limesurvey is posing any limit, because you were able to fill additional questions there. If you get exactly 41 responses again, then we really should dig deeper (how the invitations are sent, do all respondents receive the invitations, etc.).