Hello,
I updated GnuCash Portable to the latest version, 3.1.2 that came out on 6/18/18, and found that all my previously saved reports vanished and GnuCash created a new configuration directory on my C:/ drive at C:/Users/me/.gnucash. I had to restore my GnuCash Portable files from a backup in order to get my reports back. I think GnuCash has changed the way they store reports now in version 3 and this might have broken the GnuCash Portable to make it not so portable anymore. I updated from GnuCash 2.6.19 and was working on Windows 7, 64bit version. Has anybody else seen this issue?