It takes a long time for the My Cookbooks screen to load in the mobile app and sometimes it even times out and crashes the app. The My Recipes screen loads fine though.
One of your online cookbooks is causing the app to time out. That's causing your problems. It could be one of your cookbook cover photos it much too large. It could be something else.
The best way to troubleshoot is to remove some of your online cookbooks until the My Cookbooks screen can load in the mobile app. This has to be done very carefully though because syncing means to make both the same, so if you delete an online cookbook and sync, it's going to delete that same cookbook from the program on the computer.
So, the first thing you should do is go to the My MasterCook Manager screen on the computer and sign out of your online account, so nothing can sync.
Then while you remain signed out go to the Cookbooks screen in the main program on the computer and then select Refresh File List from the Tools menu to reset the syncing files.
At this point you should backup your files as explained here:
Please note you do not need to be signed into your online account to use the Backup screen in My MasterCook Manager.
Then remain signed out of My MasterCook Manager. Go to your online cookbooks web page here:
Select the Delete link next to one of your online cookbooks to delete it from your online account. Be patient. Depending on the number of recipes inside that online cookbook, it can take a bit for it to delete the online cookbook.
Then check the My Cookbooks screen in the mobile app. Does it load? If not, repeat the steps above to delete another online cookbook, and continue that process until the My Cookbooks screen loads.