Some hoses need to be reconnected to get water flowing properly.

Pretty certain it's a game issue.
You can try these, it's the same thing you are doing with disconnecting & re connection but less work:

1. Have a switch to turn on/off the power of water pumps. Turn them on when needed and off when they aren't or flick the switch off/on before use.
2. Have a water pump and switch between water barrel and sprinklers, allow the barrel to fill (or use a water jug to transfer some water.) before switching on the sprinklers. Turn them on when needed and off when they aren't or flick the switch off/on before use.
3. Skip water barrel and go water pump, water switch and pump to sprinklers. 1 water pump to 6 sprinklers (no splitters/combiners necessary)

If there isn't enough water in the pump on the first tick to get all the sprinklers/barrels going, only the ones that have enough water turn on, the others won't build up water and it just looks like it is getting the water (for sprinklers) visually look like they work (water pumps make the sounds and tools say they have water) but planters or water barrels don't fill. Water pumps only keep the information of this first tick until turned off/on again, they'l get a new amount.