Where do these lapses occur?
Here is one that I would say is textual and not translational, an issue of singular in one underlying text plural in the other.
Revelation 6:11 (NKJV) Then
a white robe was given to each of them; and it was said to them that they should rest a little while longer, until both the number of their fellow servants and their brethren, who would be killed as they were,was completed.
11 καὶ ἐδόθη αὐτοῖς ἑκάστῳ
στολὴ λευκὴ καὶ ἐρρέθη αὐτοῖς ἵνα ἀναπαύσονται ἔτι χρόνον μικρόν, ἕως πληρωθῶσιν καὶ οἱ σύνδουλοι αὐτῶν καὶ οἱ ἀδελφοὶ αὐτῶν οἱ μέλλοντες ἀποκτέννεσθαι ὡς καὶ αὐτοί. (Nestle-Aland Novum Testamentum Graece, NA28th edition)
11 καὶ ἐδόθη αὐτοῖς ἑκάστῳ
στολὴ λευκή, καὶ ἐρρέθη αὐτοῖς ἵνα ἀναπαύσονται ἔτι χρόνον μικρόν, ἕως πληρωθῶσιν καὶ οἱ σύνδουλοι αὐτῶν καὶ οἱ ἀδελφοὶ αὐτῶν οἱ μέλλοντες ἀποκτέννεσθαι ὡς καὶ αὐτοί. (based on Novum Testamentum Graece, Nestle-Aland 26th edition and The Greek New Testament, 3rd edition, UBS)
Revelation 6:11 (AKJV) And
white robes were given unto every one of them; and it was said unto them, that they should rest yet for a little season, until their fellowservants also and their brethren, that should be killed as they were, should be fulfilled.
11 καὶ ἐδόθησαν ἑκάστοις
στολαὶ λευκαὶ, καὶ ἐρρέθη αὐτοῖς ἵνα ἀναπαύσωνται ἔτι χρόνον μικρόν ἕως οὗ πληρωσονται καὶ οἱ σύνδουλοι αὐτῶν καὶ οἱ ἀδελφοὶ αὐτῶν οἱ μέλλοντες ἀποκτείνεσθαι ὡς καὶ αὐτοί (Stephanus 1550 at Bible Hub)
11 και εδοθησαν εκαστοις
στολαι λευκαι και ερρεθη αυτοις ινα αναπαυσωνται ετι χρονον μικρον εως ου πληρωσονται και οι συνδουλοι αυτων και οι αδελφοι αυτων οι μελλοντες αποκτεινεσθαι ως και αυτοι (Scriveners Textus Receptus 1894)
Now it may just be me, but the difference in meaning seems like six of one and a half dozen of the other. But that makes it all the more curious to me that they would default to the critical text, just cause?
My earliest experience with the NKJV (that I remember) was in a Sunday night Bible study. My uncle read a text from the NKJV and I was reading along in the KJV. I didn't write the text down, and I have long since forgotten where it was (but maybe Gospel of John). What he read either inserted or removed a negative (like "no" "not") making it mean the opposite from what I was reading in the KJV. I thought perhaps he misread it, and asked to look at it after class. He had not read it and the verses said opposite things. I would be pleased if I could find it again (but I'm not all that worried about it). Perhaps it was a typographical error in his particular printing of the NKJV. Those things do happen. But, if not, I cannot understand how it could have been a mere difference in translation. I have no time for continued looking up of verses in the NKJV that might be "critical-text preferred," but I have little doubt that if it was preferred in two cases that it was preferred in more. I also don't disagree with you that some of the supposed cases are mere translational differences.