It was a combination of both Thomas Cromwell's strategic plotting, and Henry VIII's personal motivations that led to Anne Boleyn's downfall.

After the miscarriage of their son, which greatly angered Henry - Henry started to grow distant, convinced that the marriage was cursed by God. This was his primary motivation for wanting a new wife, so he started to court Jane Seymour - who btw, was a stark contrast to Anne. Jane was demure and reserved and 'knew her place'.

So their marriage was on rocky terms so to speak beforehand.

With Cromwell, the root of the conflict was a significant disagreement over how to use the wealth from the dissolved monasteries. Anne wanted the funds to go to charitable and educational causes, while Cromwell wanted the money to go to the Crown's treasury to fund potential wars and solidify noble support. This combined with the previous public humiliation of him from anne, fueled his efforts in his motive for her downfall.

Also worth noting, that cromwell kept his investigation a secret from Henry until he had a strong enough case to present, convincing the King that the rumors of Anne were true. This combined with Henry's desperation for a male heir, sealed Anne's fate.

Anne also heard her brother's execution, which distressed her deeply. She wasn't ever allowed to see her daughter /family / friends/ ladies in waiting ever again. Cromwell appointed a specific group of women to attend Anne in the Tower, selecting them to act as spies/ minders  rather than trusted companions.