with version 1.3 / 1.3.1 we fixed a iOS 11 problem which is possibly the cause of partial note loss.
In some cases, when text or files are copied from another application to Bear, iOS 11 add little something called Null byte. This may cause the note to be trunked in correspondence to the byte. This has been reported to Apple and we developed a workaround for pasted and drag&dropped strings/files.
The fix in 1.3.x should avoid this problem, if you still experience data loss with this version please report it.