I find some attachment types that will open with the other IOS apps, but cause the brain to freeze completely. For example, I use iThoughts on my desktop and on my iPad. This creates .itmz files which show up as thought attachments in IOS, but rather than opening the correct app, TheBrain indicates that it is loading the file and subsequently goes into total freeze requiring force quitting and reopening. This is 100% repeatable.
I know this app is in its early stages. I can live with it not being able to open all the file types that more developed programs can, but it should not crash the program.
iMac (Retina 5K, 27-inch, Late 2015)
3.3 GHz Intel Core i5
32 GB 1867 MHz DDR3