Don't really know how to make it simpler but here goes:
ODF = Open Document Format
1. ODF (.ods, .odt files etc.) is a native format used by LibreOffice, OpenOffice, and others. If files created in that format load quickly in those applications then there is nothing wrong with those files or your Operating System/Computer.
2. ODF (.ods, .odt files etc.) is
NOT a native format for WPS, so it needs an add-in/plugin to allow it to read and write that format. See
wps-help-center
So if WPS (with the add-in installed) is having problems loading ODF files which otherwise load normally in the other programs the issue would be most probably with WPS and/or the add-in; and if the availability of internet connectivity only affects the speed of loading files in WPS but not other software, then its even more likely that the problem lies within WPS or the add-in.
Please also note that the WPS statement on the above linked page that "It can be compatible with MS Office,
which do not support ODF documents." is completely false. Microsoft Office apps do support ODF files without any additional plugins and have done so for years.