In theory you could just split your hccapx file into 779 equally large files (the size of 1 hccapx struct is also mentioned here: https://hashcat.net/wiki/doku.php?id=hccapx , it currently is 393 bytes)
The newly created files newtest.hccapx_aa etc contain the individual networks.
You could also use more advanced tools like https://github.com/ZerBea/hcxtools to extract the networks correctly (and filter them) starting with the original cap file. You can also use the tools provided by hcxtools to get information about your single hccapx files (but be aware that this is a 3rd party tool and we won't give you support about these 3rd party tools here)
Code:
split -b 393 newtest.hccapx newtest.hccapx_The newly created files newtest.hccapx_aa etc contain the individual networks.
You could also use more advanced tools like https://github.com/ZerBea/hcxtools to extract the networks correctly (and filter them) starting with the original cap file. You can also use the tools provided by hcxtools to get information about your single hccapx files (but be aware that this is a 3rd party tool and we won't give you support about these 3rd party tools here)