Did not recognize date_entered as a date\/time, it looked like 2017-10-09 13:39:49

I am facing the same issue. any solution? 

Doing a grep for the "Did not recognize" I find that it is an error that comes from the apiSave in

include/SugarFields/Fields/Datetimecombo/SugarFieldDatetimecombo.php

or

include/SugarFields/Fields/Datetime/SugarFieldDatetime.php

and in turn results from a failure of the call to the timedate function fromIso:

$date = $timedate->fromIso($params[$field]);

I tracked that to

include/TimeDate.php

public function fromIso($inputDate, User $user = null)

and it looks like it expects the format to be:

@param string $inputDate The date and time in ISO-8601 format (aka 2012-10-11T13:01:45-0700)

I hope this gives you some clues...

FrancescaS