If you check your relay list on Iris, you'll probably observe that 3 or 4 of the default relays are constantly disconnecting and reconnecting. This is what's causing posts to disappear from your feed. Delete these from your list, and then go to nostr.watch and find a few new ones to add. Add 3-4 that are geographically close to you for speed, and then add 3-4 that are in other countries that speak your native language to expand your horizons.