Bernard Muller makes an interesting case for regarding Hebrews 9.27-28 as an interpolation:

On the subject of addition, it is rather obvious that the following verses is also one of those:
Heb 9:27-28 “Just as man is destined to die once, and after that to face judgment, so Christ was sacrificed once to take away the sins of many people; and he will appear a second time, not to bear sin, but to bring salvation to those who are waiting for him.”
a) “Just as a man is destined to die once, and after to face judgment”:
Judgment to follow death is never a concept exposed in this letter. Rather, the author emphasized his contemporary faithfuls were living in the “last days” (1:2) and destined to enter “Today” (4:7) God’s rest (4:6,11) very soon “in just a very little while” (10:35-39) as “you see the Day approaching” (10:25). Then the Judgment would be applied to only the (alive) sinners and/or defectors (10:26-27,30-31,39).
b) Here Christ is offered for sacrifice but in the rest of the letter, it is Christ who is offering himself for sacrifice, such as in:
Heb 7:27b “for this He [Jesus] did once for all when He offered up Himself.”
Heb 10:5-10 and
Heb 10:12 “But this Man [Jesus], after He had offered one sacrifice for sins forever, sat down at the right hand of God”
c) “he [Christ] will appear a second time” seems to have been written to “correct” “he [Christ] has appeared once for all at the end of the ages” (10:26), only two verses earlier.
In ‘Hebrews’ Christ has no role to play during the “Day of the Lord”:
God administers the final Judgment (10:30-31,12:23), delivers the rewards (11:40) and disposes of Christ’s enemies (1:13). Meanwhile, “Since that time [the sacrifice on the cross] he [Christ] waits for his enemies to be made his footstool” (10:13).

Then, the Christians, through raptures, are to join Christ, God and angels in the heavenly Jerusalem (12:22-24). No second coming here!

However the “second coming” (on earth) will be prominently featured later on (Mt25:31-32, Ac1:11, Rev19:11-16).

Note: the notion of “second coming” did not start immediately among Gentile Christians. Paul had only a half way second coming of Jesus, down to the clouds below heaven (1Th4:16-17). This is echoed in GMark (13:26-27).