One reason could be that they still love each other but just had a misunderstanding before. Once that misunderstanding is cleared up, they naturally get back together.
There could also be a situation where they are competing with Harry for something, like a powerful magical item or a position in a wizarding organization. In their eagerness to win, they might use underhanded tactics that cause harm to Harry. For instance, they could steal his research notes related to the item, causing him to waste a lot of time and energy, and also feeling betrayed by his friends.
One great fanfiction could be 'A New Beginning for Ron and Hermione'. It shows their life after the war, how they slowly realize their feelings for each other and start a relationship. It has really sweet moments like their first date in a wizarding café.
There's 'Sooner Than Expected'. In this fic, a series of events at Hogwarts, like a shared adventure in the Forbidden Forest in their third year, makes Ron and Hermione see each other in a new light and they get together earlier. It has a lot of cute moments between them and also stays true to the overall feel of the original series.
One possible story could be that in these 10 months, Ron and Hermione are on a mission together. They face many challenges that test their relationship. Maybe they have to deal with a dark wizard threat and in the process, their bond deepens as they rely on each other's strengths.
Perhaps in the fanfiction, they get engaged in a very magical setting, like on top of a floating mountain in Bulgaria. Then they have to plan a wedding that combines both wizarding cultures, which is full of challenges and fun cultural exchanges.
It gives fans a chance to explore a different side of their relationship. In the books, not all aspects of their relationship were fully explored. Fanfiction allows for more in - depth exploration of their feelings, like how they deal with jealousy or family issues together. Also, it lets fans create their own version of a happily - ever - after for the couple. They can write about their married life, having children, and all those things that fans love to imagine.
I'm not a big fan of such dark fanfictions, but you could try looking on fanfiction.net. They have a large collection of Harry Potter fanfictions, and you might be able to find one with that plot there.
Hermione, on the other hand, could become more vulnerable yet also stronger. She has always been strong - willed, but this experience could break her down initially. However, as she copes with the miscarriage, she might find new depths to her strength. She could become more in tune with her emotions and learn to lean on Ron more, which is a change from her usually independent self. This new dynamic between them would reshape their characters as they support and grow with each other through this difficult time.