We have multiple WP Multisites which were giving our subsite administrators limited access to the plugins module. They kept getting: "You do not have sufficient permissions to access this page." We have been struggling to determine what changed and how to correct this issue. We are current on all updates from WordPress and WPMUDEV which is why we suspected a bug. We would like to share the following fix if anyone is having a similar issue with their multisite and are using the ProSites plugin.
Step1: Login as Network Admin > My Sites > Network Admin > Plugins > ProSites (Network Deactivate)
Step2: Settings > Scroll down to Menu Settings “Enable administration menus” Check off (Plugins) >Save
Step3: Plugins > ProSites (Network Activate)
Step4: Logout and log back in as subsite Admin – recheck your access.
We have performed this fix on all of our Multisites....with GRAND success. Took us a while to figure it out, but it seems to work. Hope it helps.