I have done 4 journeys on Sand Patch Grade, the couplers don't connect at all now and train brakes don't work.
What exactly are you attempting to do? Configuring everything correctly on some of these can be a nuisance.
It seems that occasionally (especially when you load a save) the couplers just lock themselves up. You will have to unlock them manually before coupling. If this is not the case, then you might have set up something wrong.
Any lights showing up upon connecting? Coupling without the alerter turned on I find doesn't keep tripping the brakes. If the brakes are stuck you have to put the reverser in neutral, full application of independent brake and automatic brake to emergency. Wait around 60 seconds and move automatic brake to release. Heard you can do an easy way like toggle the brake setting to cut-out and back to freight too. Make sure your loco is in lead/cut-in and any loco behind you is set to cut-out and trail. If your loco bounces off the wagons when coupling do use the uncouple lever thing on the wagon and try again. Might help to unlock the one on the loco too (they will lock back into place).
Pneumatic Control Switch. A parked cut of cars has an empty brake pipe; sometimes when coupling to them the airflow rate into the empty pipe exceeds the maximum allowed (the system reads it as a separation), and the control switch pops. To reset it, apply all brakes to max, reverser to neutral and wait 60 seconds. Then release the auto brake and the switch should reset (red light to your left goes off, as does the yellow HUD light). This doesn't (usually) happen in real life because the air hoses are connected manually and the angle cocks are designed not to let that happen. But TSW abstracts the hose connection.
Forgot the stream, I found out I don't know how to setup up multi units on Train Sim World 2. Any advice, I read about it but don't understand it. Is it for every route.