Secure vault not responding on iPad

Hello, any help appreciated. I set up secure vault on my iXpand 128gb usb stick then transferred filed onto it from my Mac.  It worked fine for a few times on my iPad, then for no apparent reason it froze on my iPad when I entered my correct password, with no messages, eg wrong password.

i looked at some threads on here and taking advice from these I reformatted the iXpand and downloaded the .pkg file for secure vault.  I loaded this onto the reformatted iXpand disk and set it up.  I then transferred a few files to the secure vault from my Mac and tested it on the iPad with no problems.  I then transferred a few more files from my Mac and tested it again on the iPad. The original problem happened again: after I entered the password iXpand on my iPad froze.

Has anyone any advice please as to how to solve this, or is the iXpand just a rubbish piece of kit.

many thanks in advance