How to export objects from encrypted traffic?

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I need some help exporting files from encrypted traffic. I downloaded an iso file from a website over https with wget. I also have the keys from the keylogfile. If I dump the traffic with wireshark or tcpdump and then use Wireshark 2.4.2 to decrypt it with the keyfile I can see the GET request (so decryption works to some extend) but not the file itself. Downloading over http and finding/exporting the file works nice. Also with https I can decrypt other smaller files when I download them. I don't know if this is related to the file type, size or something else. Any help appreciated.