sticking point

noun2

1. •
   A disputed issue or state of affairs that causes an interruption or outright impasse in progress towards some goal or resolution, especially in negotiation or argumentation.

   • The question of representing inside workers was a sticking point. — 1934
2. •
   (old-fashioned) The point at which a process or thing, especially a state of mind or emotion, reaches its greatest strength and remains steadfast; sticking-place.

   • It warmed his feelings to the sticking point. — 1842