Hi Giuliano!
First, as general interest, when you update version there is no need to do adif operations if the computer remains same.
Logs are in ~/.config/cqrlog folder (if you have not selected external database server to store your logs).
Then even uninstal of Cqrlog will not remove your logs.

When you imported adif, did you get any errors?
2.6.0 has very good error file in imports that tells the reason.

In case there were no errors and import did just stop before end reason is usually wrong special character in some qso record.

Find last imported qso from Cqrlog. Then make a copy of your adif file and open it with text editor. With editor's search locate that last imported qso record. A record ends to "<eor>" . Look at next record if you see any special character like ones that have "hat" over letter.(usually in name or qth) If found remove them, save and try to import again.

If you can't find any of them simply erase the qso record that is first not imported, ( all text between two "<eor>" .), save file and try import again.

Reason for this is that older Cqrlogs did not use INTL adif tags for things having special characters and so adif tags length do not fit character count as special character takes two bytes but shows only on letter.