Reading a dossier in the Science & Vie magazine.

When it was launched, we were told Pioneer 10 would reach Aldebaran 2,000,000 years from now.....

But then, in 1980, an anomaly was discovered.

Pioneer 10 is presently 400,000 km behind were it should be, or 3 hours too short. Pioneer slows down.

If the anomaly persists, in 500,000 years, Pioneer 10 will stop relative to the Sun and will thus never reach Aldebaran.

The anomaly also affects Pioneer 11. No mention of Voyager 1 and 2 and that has to do with their 3 axis stabilization (making it harder to exactly point where they are).

Another anomaly affected Galileo, Cassini, Near, Rosetta...not in deep space but every time they flew by the Earth, they gained a faster speed than expected.
Comets almost always arrive at perihelium several days in advance with the predicted time. And Halley is now slightly behind its expected location.

Scientists are quite excited...Maybe general relativity has a flaw somewhere.