“Our top members have drifted away, but I’m hoping after [take action] they will come back sharing knowledge again”
I’ll predict that won’t happen.
Moz had this problem too. Top SEO talent used to love participating in the community. The top members built a strong following and launched their own blogs/communities.
They occasionally return to participate, but only on posts about them, in webinars where they’re the guest star, to write special guest posts, or to participate in speaking at events etc…
Top members don’t usually drift away because of a single tech issue. They drift away because they’re relationship and attitude towards the group has changed. A sudden change might precipitate that issue, but the wheels were already long in motion. They feel their status is above this group level.
Don’t try to bring them back to perform the same behaviors, try to bring them back to do something different – something more befitting their perceived status (in their eyes) today.
It’s rarely a good idea to reach back into the past for community ideas. So look ahead and design new ways for people to participate in the group. Ways with high status and provide a sense of challenge.