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Stinking Toilet at times

Hi there, My master bedroom attached bathroom/toilet smell like sewer at certain times, mainly in the evening and early morning. I have tried cleaning the toilet, floors and other nook and corners but it really smells like gas coming from sewer. This is not happening always, which is strange. Mostly happening at night. No issues with other bathrooms/toilets. Can somebody help me with this? Have you seen this type of issues and fixed this before ? Is this something to do with some sort of broken seal ? Started happening before 2 months. Looking to find the root cause and fix this ASAP. Looking for someone experienced in fixing this specific problem