Thank you for the detailed feedback — this is exactly the kind of thing that's hard to catch as the solo dev!
On the button issue: you found a real bug. Hovering triggered a 1px "lift" animation that could physically move the button out from under your cursor, causing it to rapidly flicker between hover/not-hover (and only register clicks during the "hover" frames) — especially if your cursor rested near the bottom edge of a button. Fixed in the build I just uploaded by removing that lift effect entirely.
On difficulty: also a fair catch, and it's related to something another player flagged too. Raid strength used to scale only with wave number, so early raids could feel arbitrary (and low-stakes either way), while a player who invested heavily in walls would rapidly outscale the raids and stop feeling any tension. I've adjusted it so raid strength also scales with your current defense investment — the early game is untouched, but the more you stack defense, the more the raids scale to match, so it should stay a meaningful threat instead of becoming a non-issue a few minutes in.
Invasion depth and UI information density are both fair calls for this early a build — noted for the roadmap as the game gets more fleshed out. Really appreciate you taking the time, and glad you got some enjoyment out of it already!