Is delaying prayer past its time considered an act of disbelief (kufr), and is one who intentionally misses Fajr prayer every day required to pronounce the Shahada anew to re-enter Islam?

Intentionally abandoning prayer is a grave evil and a major sin by scholarly consensus. It is a greater sin than adultery, theft, drinking alcohol, and taking a life. Some scholars hold that one who intentionally abandons prayer is an apostate, outside the fold of Islam, though the more accepted view is that it is not disbelief that expels one from the religion. What you have mentioned is not an excuse that permits you to abandon prayer; rather, it is a result of yielding to obsessive whispers (waswas). Repent to your Lord for this grave sin. Strive against these whispers and disregard them, for ignoring them is the best treatment. Opening the door to waswas leads to corruption in both religious and worldly matters. Do not prolong your stay in the restroom after relieving yourself, do not excessively wash limbs, and do not repeat any act of worship you have already performed simply due to obsessive whispers.