Okay I found what seems to be the problem. On the file that shows the error
(nano /usr/lib/yum-plugins/changelog.py), there is the following line 215
if self._since_dto == dateutil_parser.parse('garbage', fuzzy=True):
# 'since' was a package name, not a date
extcmds.insert(0, since)
If i change the ‘garbage’ variable to 2017-Dec-29 as it follows
if self._since_dto == dateutil_parser.parse('2017-Dec-29', fuzzy=True):
# 'since' was a package name, not a date
extcmds.insert(0, since)
If I do this, everything is working fine and updates are working correctly. For what i can see, the argument provided plain text is not a date so thats why it shows the error