A DASH wallet can contain many private keys and their corresponding DASH addresses "X..." The balance your wallet shows is the sum of all DASH held on these addresses, so potentially the balance is made of of many smaller amounts (sub-balances).
When you ask your wallet to send any amount of DASH to somewhere (e.g. the CrowdNode deposit address) the default behavior is to combine DASH from these addresses in the wallet in such as way as to minimise the total transaction size (in bytes) and thus minimise the transaction fee.
This means that the default wallet behavior does not ensure that at least part of your deposit comes from the DASH address you have registered with CrowdNode and if it doesn't our system cannot credit the deposit to you.
One simple way to solve this problem is to first "tidy up" your wallet by collecting all sub-balances on a single DASH address (the one you've registered with CrowdNode). This is what it means to send to yourself. You're collecting all your DASH an a single address. After that, you can deposit (any amount you wish) to CrowdNode. This ensures that the system credits the deposit to you.
(The more advanced solution is to use "coin control" in wallets which support it such as DASH CORE and force the wallet to use DASH from your registered DASH address).