Explanation of this behavior:
In monitor mode the adapter does not check to see if the cyclic redundancy check (CRC) values are correct for packets captured, so some captured packets may be malformed.
The device is able to detect the Physical Layer Convergence Procedure preamble and is able to synchronize to it, but there is a bit error in the payload.
This can lead to unexpected results.
By latest commit, hcxpcapngtool will detect some kinds malformed packets (unfortunately not all) and inform the user in Wireshark manner:
...
malformed packets (total)..............: 266
BROADCAST MAC error (malformed packets): 163
IE TAG length error (malformed packets): 54
ESSID error (malformed packets.........: 35
EAPOL messages (malformed packets).....: 23
Malformed packets detected!
"In monitor mode the adapter does not check to see if the cyclic redundancy check (CRC)
values are correct for packets captured. The device is able to detect the Physical Layer
Convergence Procedure (PLCP) preamble and is able to synchronize to it, but there is a
bit error in the payload. This can lead to unexpected results."
Please analyze the dump file with Wireshark.