dogs suddenly not getting on together.

[Goya]

Opinions/advice needed please.
I have 3 dogs, 2 speyed bitches and 1 neutered dog. J and S (the girls) have been together for 4 years and M (dog) joined us a year ago.
has anyone ever experienced a sudden onset of "spats" between the 2 bitches? I say spats but it is one of them suddenly picking on the other for no apparent reason.
This has happened a couple of times over the last 3 days. As I said there is no apparent reason.
Once was when they were on a walk. We had just gone through a gateway and J suddenly ran back and had a go at S.
Then last night at bedtime the same happened--she just had a go at S.
I am puzzled and obviously a bit worried.
The dog M, is not involved at all--he just goes on his merry way.

 

[CorvusCorax]

That's why they're called bitches

Did both of these incidents happen near a gate/doorway or just one?
Entry and exit points can be flashpoint areas between animals jostling for pecking order - I would control who comes through doorways and how, and see if that makes a difference, calm, polite, no charging or pushing x

 

[Goya]

Good point, thank you. Yes, the walk one was just through a gateway and the bedtime one was by the bedroom door.
It is just so strange that it is happening all of a sudden, that's what puzzled me.
Another thought is that J is very unsettled at the mo, due to those darned fireworks. I suppose this might be another reason she is behaving out of character.