Do you have community plug-ins enabled? I found the same extremely painful problem until I created a separate config folder. On the mobile version go to setttings > About > Advanced and override config folder to something else. In my case, I just call it .obsidian-mobile
My mobile config only uses a couple of plug-ins that are important as the majority are only needed on desktop. That made all the difference in the world for me and now the app fully syncs in a few seconds.