Could you please specify what wave this usually happens on? (wave number is displayed on the end point of the path)
The highest I've gotten is wave 30, and that was with the strategy of using 5 turrets and spreading out upgrades evenly between them. Which results in me only being able to level them up once (50xp + 50g each) and being able to spend 150g on crank-action upgrade for just 2 of them before I die.
not investing in the first level up to save the 250g cumulative gold causes you to get overrun around wave 15-18 as your turrets can't even kill one thing with their abysmal fire rate, combined with being no longer capable of one-hitting red blips anymore.
All the upgrade options are there, but at the current state, the player never gets a chance to pick them up.