APFS, fsck_apfs and 'physical extent corruption' - what's up with my MacBook Pro?

So, this morning I ran First Aid on my SSD and found that my local snapshots had a bunch of extent ref mismatches. I made sure my Time Machine back-ups were up to date, then removed the snapshots using tmutil. I then let Time Machine create a couple more local snapshots and ran First Aid again, and found the same problem in First Aid.

To try and fix the issue I ran Internet Recovery and ran First Aid from there, and while the issues were found, fsck_apfs is reporting "warning: found physical extent corruption but repairs are disabled". It then reports "The volume /dev/rdisk2s1 appears to be OK," which sounds like a contradiction.

Can anyone shed any light on what's up with the 'physical extent corruption'? Thanks!!

For reference, last week I installed the combo update for 10.14.4.

Full output from First Aid (well, fsck_apfs, really):

Running First Aid on “MBP4 HD” (disk2s1)

Repairing file system.

Volume was successfully unmounted.

Performing fsck_apfs -y -x /dev/rdisk2s1

Checking the container superblock.

Checking the EFI jumpstart record.

Checking the space manager.

Checking the space manager free queue trees.

Checking the object map.

Checking volume.

Checking the APFS volume superblock.

The volume MBP4 HD was formatted by newfs_apfs (748.21.6) and last modified by apfs_kext (945.250.134).

Checking the object map.

Checking the snapshot metadata tree.

Checking the snapshot metadata.

Checking snapshot 1 of 2.

error: Cross Check : Mismatch between extentref entry reference count (1) and calculated fsroot entry reference count (0) for extent (0xa9697f7 + 362927)

error: Cross Check : Mismatch between extentref entry reference count (1) and calculated fsroot entry reference count (0) for extent (0xaa1f949 + 65528)

error: Cross Check : Mismatch between extentref entry reference count (1) and calculated fsroot entry reference count (0) for extent (0xaa4fa4d + 27648)

error: Cross Check : Mismatch between extentref entry reference count (1) and calculated fsroot entry reference count (0) for extent (0xaa9e8ea + 524224)

error: Cross Check : Mismatch between extentref entry reference count (1) and calculated fsroot entry reference count (0) for extent (0xabf039b + 1056)

Checking snapshot 2 of 2.

error: Cross Check : FSroot tree references extent (0xaa2f941 + 8191) which is not present in the ExtentRef tree

error: Cross Check : FSroot tree references extent (0xaa31940 + 1388) which is not present in the ExtentRef tree

error: Cross Check : FSroot tree references extent (0xaa5664d + 4608) which is not present in the ExtentRef tree

error: Cross Check : Mismatch between extentref entry reference count (0) and calculated fsroot entry reference count (1) for extent (0xaa2f941 + 8191)

error: Cross Check : Mismatch between extentref entry reference count (0) and calculated fsroot entry reference count (1) for extent (0xaa31940 + 1388)

error: Cross Check : Mismatch between extentref entry reference count (0) and calculated fsroot entry reference count (1) for extent (0xaa5664d + 4608)

Checking the extent ref tree.

Checking the fsroot tree.

error: Cross Check : Mismatch between extentref entry reference count (0) and calculated fsroot entry reference count (1) for extent (0xaa2f941 + 8191)

error: Cross Check : Mismatch between extentref entry reference count (0) and calculated fsroot entry reference count (1) for extent (0xaa31940 + 1388)

error: Cross Check : Mismatch between extentref entry reference count (0) and calculated fsroot entry reference count (1) for extent (0xaa5664d + 4608)

Verifying allocated space.

Performing deferred repairs.

warning: found physical extent corruption but repairs are disabled

The volume /dev/rdisk2s1 appears to be OK.

File system check exit code is 0.

Restoring the original state found as mounted.

Operation successful.