It'll be a chafed wire in the harness running to the trunk lid. You'll find the harness on the right hand (looking forwards) trunklid hinge. I't's partly covered by a semi rigid plastic sheath to protect it but this does fail eventually. Remove the loom tape, find the broken wire(s), solder them back together then re-tape the harness, repairing/replacing the plastic sheath as necessary.
You'll probably find that the broken wire(s) are touching when the trunk lid is open, but then part company when the lid is shut rendering the release buttons useless.
Mine went a couple of years ago and I noticed that the trunk lights came on when the trunk began to open then went off when it was opened fully. This eventually blew a fuse and I couldn't get the car out of park! (same fuse). Since that repair, I had a problem when the trunk would open from the remote or from the dash release, but not from the trunk lid button itself! Have now repaired and improved the harness protection so am hoping for a lasting trouble free period!!