OK I have repeated the process on a new system and here are the logs. First I installed a minimal system offline, with DISTRIB_DESCRIPTION="Debian GNU/Linux installer" DISTRIB_RELEASE="9 (stretch) - installer build 20161212-00:04" on a USB stick.
Then I went online and installed more and more packages. Here you can see a birds eye view, 48 matches in 26 lines for "insserv" in buffer: *compilation* 1216:Selecting previously unselected package insserv. 1217:Preparing to unpack .../06-insserv_1.16.0-5_amd64.deb ... 1218:Unpacking insserv (1.16.0-5) ... 4803:insserv: fopen(/etc/insserv.conf): No such file or directory 5476:insserv: fopen(/etc/insserv.conf): No such file or directory 5536:insserv: fopen(/etc/insserv.conf): No such file or directory 5764:insserv: fopen(/etc/insserv.conf): No such file or directory 5770:insserv: fopen(/etc/insserv.conf): No such file or directory 5774:insserv: fopen(/etc/insserv.conf): No such file or directory 5823:insserv: fopen(/etc/insserv.conf): No such file or directory 5824:insserv: fopen(/etc/insserv.conf): No such file or directory 5869:insserv: fopen(/etc/insserv.conf): No such file or directory 5905:insserv: fopen(/etc/insserv.conf): No such file or directory 5961:insserv: fopen(/etc/insserv.conf): No such file or directory 6022:insserv: fopen(/etc/insserv.conf): No such file or directory 6055:insserv: fopen(/etc/insserv.conf): No such file or directory 6127:insserv: fopen(/etc/insserv.conf): No such file or directory 6130:insserv: fopen(/etc/insserv.conf): No such file or directory 6131:insserv: fopen(/etc/insserv.conf): No such file or directory 6287:insserv: fopen(/etc/insserv.conf): No such file or directory 6328:insserv: fopen(/etc/insserv.conf): No such file or directory 6361:insserv: fopen(/etc/insserv.conf): No such file or directory 6367:insserv: fopen(/etc/insserv.conf): No such file or directory 6417:insserv: fopen(/etc/insserv.conf): No such file or directory 6576:insserv: fopen(/etc/insserv.conf): No such file or directory 6607:Setting up insserv (1.16.0-5) ... of what is happening. We see the problem only occurs between the time insserv has been unpacked, and when it is finally set up. After it has been set up, the problem no longer occurs, for many days afterwards so far. Here are the logs,
apt.log.gz
Description: *compilation* buffer
