From my notes these are the changes in the 4.39.23027 and 4.38.23038 firmware releases. The 4.39 release is for the Libra Colour, Clara Colour and Clara BW models. The 4.38 release is for the rest of Kobo's touch ereaders.
Changes:
Updated certs
Updated Analytics
Disable telnet access (still works using NickelMenu to enable)
Fixes:
Store crashes
Database not closing properly
Kobo Plus content consumption readings
Adjust Kobo Plus audiobook sessions along with idle time
Missing translations
I tested about 100 disconnect, read & connect cycles on my Sage and no database corruption was seen.