Contradiction with Matthew 28:20
While Acts 20:38 speaks about not seeing Paul's face anymore, Matthew 28:20 promises Jesus' presence "always, even unto the end of the world."
Matthew 28:20: Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, [even] unto the end of the world. Amen.
Contradiction with John 14:18
Acts 20:38 suggests separation, but John 14:18 reassures that believers will not be left comfortless.
John 14:18: I will not leave you comfortless: I will come to you. [comfortless: or, orphans]
Contradiction with Hebrews 13:5
Acts 20:38 mentions not seeing Paul's face, whereas Hebrews 13:5 promises that God will never leave nor forsake believers.
Hebrews 13:5: [Let your] conversation [be] without covetousness; [and be] content with such things as ye have: for he hath said, I will never leave thee, nor forsake thee.
Contradiction with 1 Thessalonians 4:17
While Acts 20:38 implies a permanent separation, 1 Thessalonians 4:17 speaks of believers being "caught up together" forever.
1 Thessalonians 4:17: Then we which are alive [and] remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
Contradiction with Revelation 22:4
Acts 20:38 talks about not seeing someone again, yet Revelation 22:4 promises believers will see God's face.
Revelation 22:4: And they shall see his face; and his name [shall be] in their foreheads.