Unfortunately many ZCash wallets have not implemented ZIP-317 or even orchard addresses. The result is that funds cannot be sent from these wallets because the transaction will never be confirmed and accepted by the ZCash network. This issue can be resolved by installing ZCash Wallet.

Why does this ZCash transaction issue occur?

The root of the problem is an improper transaction fee being set in the wallet. The last year the ZCash network has been under a spam attack. This motivated the the development of ZIP-317 which is a set of rules for setting transaction fees. The hope was that it would reduce the effectiveness of the spam attack.

The problem is that many ZCash wallets are not well maintained, so have not been made compatible with ZIP-317. Since transactions created with those wallets do not create transactions with high enough fees it results in a situation where transactions cannot be confirmed.

Solution: how to properly send transactions

Install ZCash Wallet and import the mnemonic / seed used by the wallet with the stuck funds. Ensure to input the number of shielded addresses used by your other wallet. Once the wallet syncs you will have access to funds and the ability to send transactions with the correct fees.