Most all of us have had issues but have learned what works best for our particular situation. For me I use a septic system approved TP, always use plenty of water and have the auto level set to ever so slightly tilt the RV so the toilet is on the high side.
With all that said your problem sounds more severe than the rest of us. It is possible your vent pipe is slid too low into the holding tank. If you take the vent cover off the top of your sewer vent you should be able to see the vent pipe. It sits inside an outer pipe and may be simply set too low. You may be able to tell by looking. If that is your problem it will likely require a trip to the dealer. In the meantime, try the items mentioned above and empty the tank often.
Side note...I have a 2016 Miramar 34.4 and taking the steps above I have no problems.
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