Why did the USD-value of my tokens drop after withdrawal?
When you contribute tokens to a liquidity pool, your assets are susceptible to impermanent loss, which occurs because of a change in the price of your assets. Make sure to read more about impermanent loss before adding liquidity.
Is there any restriction on the distribution of farm yields?
You can withdraw your farm yields at any time. The same rule applies to liquidity; you can withdraw your LP tokens without any lock-in periods or early-withdrawal penalties.