This happened to me after I manually changed @ to @bad and renamed the last working @apt snapshot backup to @ 

as 

sudo apt-btrfs-snapshot list
Available snapshots:

listed 0 snapshots !!!

while

sudo btrfs sub list /
ID 257 gen 15248 top level 5 path @bad
ID 265 gen 2060 top level 5 path @apt-snapshot-2018-12-29_20:36:25
ID 268 gen 15247 top level 5 path @apt-snapshot-2018-12-29_21:12:34
ID 270 gen 15247 top level 5 path @apt-snapshot-2018-12-29_21:45:56
ID 272 gen 15247 top level 5 path @apt-snapshot-2018-12-29_22:01:38
ID 273 gen 15247 top level 5 path @apt-snapshot-2018-12-29_22:23:44
ID 275 gen 15247 top level 5 path @apt-snapshot-2018-12-29_22:36:06
ID 276 gen 15247 top level 5 path @apt-snapshot-2018-12-29_22:49:29
ID 277 gen 15247 top level 5 path @apt-snapshot-2018-12-29_22:56:47
ID 279 gen 15247 top level 5 path @apt-snapshot-2018-12-29_23:06:23
ID 280 gen 15247 top level 5 path @apt-snapshot-2018-12-29_23:34:56
ID 281 gen 15247 top level 5 path @apt-snapshot-2018-12-29_23:40:52
ID 282 gen 15247 top level 5 path @apt-snapshot-2018-12-29_23:41:16
ID 283 gen 15247 top level 5 path @apt-snapshot-2018-12-29_23:44:19
ID 285 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:14:56
ID 286 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:18:54
ID 288 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:34:49
ID 289 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:38:10
ID 290 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:39:34
ID 291 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:40:18
ID 292 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:49:49
ID 293 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:52:48
ID 294 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:53:03
ID 295 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:55:10
ID 297 gen 15247 top level 5 path @apt-snapshot-2018-12-30_05:57:49
ID 298 gen 15247 top level 5 path @apt-snapshot-2018-12-30_06:13:19
ID 299 gen 15247 top level 5 path @apt-snapshot-2018-12-30_06:20:02
ID 300 gen 15247 top level 5 path @apt-snapshot-2018-12-30_06:26:21
ID 301 gen 15247 top level 5 path @apt-snapshot-2018-12-30_06:34:00
ID 302 gen 15247 top level 5 path @apt-snapshot-2018-12-30_06:47:18
ID 303 gen 15217 top level 5 path @apt-snapshot-2018-12-30_06:52:49
ID 304 gen 15295 top level 5 path @
ID 306 gen 15247 top level 5 path @apt-snapshot-2018-12-30_07:15:54
ID 307 gen 15247 top level 5 path @apt-snapshot-2018-12-30_07:16:20
ID 308 gen 15247 top level 5 path @apt-snapshot-2018-12-30_07:20:41
ID 309 gen 15247 top level 5 path @apt-snapshot-2018-12-30_07:33:28
ID 310 gen 15247 top level 5 path @apt-snapshot-2018-12-30_07:33:52
ID 312 gen 15247 top level 5 path @apt-snapshot-2018-12-30_07:34:18
ID 313 gen 15247 top level 5 path @apt-snapshot-2018-12-30_07:35:29
ID 314 gen 15248 top level 5 path @apt-snapshot-2018-12-30_07:38:02
ID 315 gen 15247 top level 5 path @apt-snapshot-2018-12-30_07:41:40


sudo btrfs sub show /
@
	Name: 			@
	UUID: 			3b347b10-bc32-f848-89c5-8c6c6585c4f2
	Parent UUID: 		e7bfca0b-0e56-454c-a96a-7310eb784685
	Received UUID: 		-
	Creation time: 		2018-12-30 07:13:22 +1000
	Subvolume ID: 		304
	Generation: 		15296
	Gen at creation: 	14513
	Parent ID: 		5
	Top level ID: 		5
	Flags: 			-
	Snapshot(s):