This warrants a vet visit. I'd record a video of the problems if they happen again so the vet can use the video in their examination and diagnosis. I'd consider this fairly urgent because he's a breed prone to spinal issues, which can impact leg function.
Unfortunately no one here can give you anything more specific, and it's against rules to guess at a diagnosis or advise any treatment for an issue that hasn't been seen by a vet. This is to protect you and your dog, because even well-meaning medical advice can be very dangerous in the wrong situations. I wish you luck, please let us know what the vet says!
Unfortunately no one here can give you anything more specific, and it's against rules to guess at a diagnosis or advise any treatment for an issue that hasn't been seen by a vet. This is to protect you and your dog, because even well-meaning medical advice can be very dangerous in the wrong situations. I wish you luck, please let us know what the vet says!