Keef
Never trust an ADF, especially at night, or near the coast
You are right about the coastal effect; I see a 20deg shift appear and disappear over a distance of about 2 miles when doing one NDB/DME procedure at an AD with pretty high ground around it.
I once asked an instructor (who had a frozen ATPL) what he would do if the ADF was telling him he was OK, but a GPS was telling him he was going to die. He said he would trust the ADF. This is the correct official reply.
What's the solution? The solution for me would be to go somewhere with an ILS.