Instagram: No access to Moments? Only small subset of albums? All Photos album incomplete?

On my iPhone 6 (running iOS 8.3, Apple's Photos app, iCloud Photo Library enabled) I am experiencing issues using Instagram (and some other apps):

From the Instagram app, I find that I have no access to "Moments". From other iOS apps (Pixelmator, Camera+) I do have access to Moments, however. So why not from Instagram?

However, Instagram gives me access to some albums - but only to a small subset of them (shown in some inexplicably random order, btw) including the "All Photos" album. To make things even worse, the "All Photos" album only contains just some 10 % (2,150) out of the 22,000+ photos I have. So what's going wrong here with Instagram and Apple's Photos App?

(Sure I see that I should ask Instagram. However, I am confident that the clever guys here at Apple might be much more capable to give a knowledgeable answer, or even a solution ... Thank you in advance. 😉 )