seeds rotten inside fruit

I've got a Roma tomato plant. When I cut open the ripe fruit, I find that some of the seeds have started to rot with signs of fungus. The fruit looks perfect from the outside and the flesh looks good, but I'm not tempted to eat them. I know the soil isn't great and they didn't get as much sun as I hoped. I'll plant them in a different location next year, but any idea what may have caused this? Thanks
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i like to pick my roma,s early and let them ripen to my likeing
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