Smell of Sewage in Basement Apartment

I have been trying to figure out this problem for months but no one seems to know the answer.

I live in a basement apartment that is hooked to a septic system. For a few months now, we have been experiencing a sewage smell in the apartment. I have smelled all the drains and nothing seems to be coming from them.

Under our stove in the kitchen we have an opening in the floor that leads to a pump that pumps our water/waste up and out of the basement. I believe I have tracked the smell down to this area.

The smell is worse when the pump goes off multiple times in a row (ex: taking a shower). It is also worse near the end of the day (presumably because the pump has been going off multiple times throughout the day).

The tank was emptied about 9-10 months ago and the smell started ~4-5 months ago.

This problem is very frustrating and no one seems to be able to help me. Any advice would be appreciated.

Can you see the vent from the sewage ejector pump? Maybe something has come loose since the pump was worked on. Either that or you have an improperly vented drain line somewhere and one of your traps may be being sucked dry when the pump goes on. Or maybe you have a floor drain somewhere and the trap primer has gone bad? This will allow they trap to go dry and sewer gas can come up through the drain. Just a few wild guesses..