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Limited information is provided, but the most likely cause is explained many times here; for example:

1. https://ask.wireshark.org/question/20865/80211-only-partially-decrypted/#20876
2. https://ask.wireshark.org/question/10499/persistent-problems-with-wireshark-capturing-wlan-high-datarate-frames/#10519
3. https://ask.wireshark.org/question/2861/airpcap-no-ip-traffic/#2864

All of these are related to same root cause: capture envelope not large enough to capture traffic under review. Data frames are highly modulated, while control/management are not and therefore are easier to pick up.

The RTL8812 devices are not great, but can collect traffic. Is it configured correctly - especially in context to channel width (20/40/80)? Could be your traffic under review is 11ax, and you are trying to capture with a 2x2 11ac adapter? Perhaps capture is too far away to collect highly modulated frames? There is a sharkfest presentation from a couple of years ago on the topic: https://www.youtube.com/watch?v=p3Ik_pcwp9c