One Mercury Astronaut flying wet. Launch was delayed and nature wouldn't wait. On that particular flight there were no provisions for the astronaut's body wastes.
Retro rockets weren't jettisoned as planned on another flight because telemetry indicated the air bag between the capsule and the heat shield was released while still in orbit. "Plan B" was to use the retro rocket to hold the heat shield in place. Either the air bag deployed indication was wrong (more likely) or "plan B" held the heat shield in place.
Another Mercury spacecraft sinking between spashdown and recovery. Astronaut nearly drowned.
A Gemini capsule tumbling out of control with a malfunctioning attitude control thruster.
Three astronauts burning up when the interior of the capsule caught fire.
A lander overshooting the intended landing site and nearly running out of propellants because the computer was overwhelmed with data from a tracking radar that was unnecessary at that stage of the flight. A vital circuit breaker had to be poked with a pen barrel after its handle was broken off.
A lightning strike when a moon rocket was launched trough a thunder cloud. Momentary complete shutdown of all the spacecraft electrical systems.
The very next Apollo flight a liquid oxygen tank essentially destroyed the service module. Crew barely made it back alive.
Not quite what I consider trouble free.