The minimum nomination amount needed to earn rewards is now dynamic, and can be found on the Targets page: 

Bags List

With the recent runtime upgrade to 9170, we saw the implementation of what's called a "bags-list". This is done to achieve an ordered list of nominators within the constraints of the relay chain runtime. It allows the bonding minimum to be lowered to a dynamic minimum, instead of a fixed amount of DOT. You can read more details about the bags-list feature here.

If you are staking over the minimum amount and still aren't receiving rewards, your address may need to be re-positioned in the bags list. This happens because bags are sorted based on stake, but the accounts in each bag are not. So, in the last bag only the first X accounts will participate in the election. But since the accounts aren't ordered based on stake, it's possible that accounts with higher than the minimum amount excluded, because they found themselves lower in the bag.

Accounts can put themselves in front of other accounts with lower stake in the same bag using the voterList.putInFrontOf extrinsic. It's important to note that this process only puts you in front of an account that has lower stake. Therefore the process doesn't guarantee that you will start getting rewards, since it's possible that your address may be put in front of an account that itself isn't included in the set.

Polkadot-JS UI

1. Make sure your stash account is active, then navigate to the Bags page and select My bags. (This example is on the Westend testnet but the result will be the same on Polkadot).

If you see a button that says Rebag in place of the highlighted button below, this indicates that your account is in currently placed in the wrong bag. Perform this action first if needed, which will move your account to the correct bag. Then proceed to Step 2.

2. When you see the following highlighted button, this means your account is in need of re-positioning. Select it to issue the extrinsic.

3. Next, sign & submit the transaction.

This will realign your position within the bag and hopefully allow you to begin receiving rewards again!