iMessage group chats merging, disappearing, and renaming

iMessage keeps combining group chats. We created 2 separate group chats for work. While they have the same people in each chat, they were named differently and for years they were kept separate. To keep it simple for this explanation they are named chat 1 and chat 2. Over the past year they will randomly combine on some peoples phones or sometimes completely disappear all together. So I’ll open my phone and it will only show chat 1 and chat 2 will be missing. I’ll scroll through it and realize things I send in chat 2 the previous day will show up in chat 1. Then later in the day someone who has both chats on their phone will text in chat 2 and when I go to check I’ll have both chats again completely separate. It’s also showing that people keep renaming the chats when nobody has renamed anything. We also tried removing one person from one of the chats so they didn’t have the same number of people but that ultimately led to the chats being combined randomly again and kicking that person out of both chats. Hopefully that wasn’t confusing.