ClamAV-daemon crashes trying to read amavis-new files

ClamAV-daemon 0.99.2+dfsg-0ubuntu0.16.04.2 and amavis-new installed per these instructions: ://help.ubuntu.com/community/PostfixAmavisNew

Crashes on attempting to read amavis-new files. Note that clamav is a member of group amavis, and has execute access to all directories in the file path through that group.

Log entries such as below appear on receipt of any email:

Sep 28 20:24:15 localhost amavis[7738]: (07738-03) (!)run_av (ClamAV-clamd) FAILED - unexpected , output="/var/lib/amavis/tmp/amavis-20170928T125358-07738-X0fhwQmJ/parts: lstat() failed: Permission denied. ERROR\n"
Sep 28 20:24:15 localhost amavis[7738]: (07738-03) (!)ClamAV-clamd av-scanner FAILED: CODE(0x31b2928) unexpected , output="/var/lib/amavis/tmp/amavis-
20170928T125358-07738-X0fhwQmJ/parts: lstat() failed: Permission denied. ERROR\n" at (eval 100) line 905.
Sep 28 20:24:15 localhost amavis[7738]: (07738-03) (!)WARN: all primary virus scanners failed, considering backups

The clamav user can certainly access the directory in question (note the directory is, in fact, empty):

clamav@localhost:/var/lib/amavis/tmp/amavis-20170928T125358-07738-X0fhwQmJ/parts$ ls -la
total 8
drwxr-x--- 2 amavis amavis 4096 Sep 29 00:22 .
drwxr-x--- 3 amavis amavis 4096 Sep 28 12:53 ..
clamav@localhost:/var/lib/amavis/tmp/amavis-20170928T125358-07738-X0fhwQmJ/parts$