Two things:
1. Delete your map cache. You shouldn't be discovering so much at once, and that issue is usually solved by doing that. You should only be discovering what other members of your tech group have discovered, and only 25-200 years afterwards
2. If you like a slow spread of discoveries, set "spread of land/sea provinces" up to 200 years before you start a game. That'll mean you won't start making any 'automatic' discoveries for a long time.
1. Delete your map cache. You shouldn't be discovering so much at once, and that issue is usually solved by doing that. You should only be discovering what other members of your tech group have discovered, and only 25-200 years afterwards
2. If you like a slow spread of discoveries, set "spread of land/sea provinces" up to 200 years before you start a game. That'll mean you won't start making any 'automatic' discoveries for a long time.