Looking at the DOGE vault here: https://blockchair.com/dogecoin/address/D5dg3Z6hN3pEuBrocL3ewgwrreFBU4JbXa
There are a surprising number of unconfirmed transactions:
Currently there are 15 unconfirmed transactions. The earliest unconfirmed transaction is timestamped 2021-01-30 and the most recent is 2021-02-04.
Every one of these transactions has a transaction fee of less than 1 DOGE. Transactions with a fee of less than 1 DOGE will never be mined. The 1.14 softfork which activated this past fall eliminated 0 DOGE and <1 DOGE transactions fees.
Strongly recommend updating the code which transfers from the shielding address to the vault to include a transaction fee minimum check that ensures all vault transfer transactions have at least a 1 DOGE fee.
As is, these 15 transactions will remain in the mempool for ~14 days, at which time they will expire. The funds should transfer back to the shielding address.
It is possible to rebuild an unconfirmed vault transfer as a RBF transaction with >1 DOGE fee, using the private key of the shielding address. This should allow the higher RBF fee transaction to be picked up by a miner and complete the transfer. The older, low fee transaction will become a (rejected) double-spend should a miner try to include it in a block before it expires out of the mempool.
I do note that transfers of DOGE from shielding address to vault also have the same deducted fee issue I noted with the Litecoin vault.