There could be so many reasons to it. But yes, new species can withhold a female guppy to not deliver her fry (or all her fry). But that depends on the kind of fish the others are. And I don't mean their species but their behavior.
what other parameters should i list?
water parameters and such have not changed since the beginning.
plants have grown a lot more lush since then.
I have added Pearl Gouramis and Harlequin Rasboras