When I try to Bookmark my tabs into a group, some tabs end up missing. I've tried adding them individually to the group but it still doesn't work. Help?

I need to group some tabs in my Bookmark section. I have never been able to group all of my tabs into one group. It's so random. Sometimes, I'll be able to fit five tabs into a group without missing a tab; and other times, several tabs will be missing in the group. At those times, I try to add the tabs' link individually into to the group - but that doesn't work because that will either open up a blank page when I open up the Bookmark group or lead to a broken link. Even if I've tested the link prior to make sure it works. This is so aggravating. I hate having several hundred individual tabs in my Bookmarks, I really want the group option to work.