(70007)The timeout specified has expired: ... AH01991: SSL input filter read failed

Issue

What does "SSL input filter read failed" mean?

[Tue Mar 14 14:36:39.114982 2017] [ssl:info] [pid 1621:tid 139781198710528] [client 127.0.0.1:60678] AH01964: Connection to child 10 established (server example.com:443)
[Tue Mar 14 14:36:39.127948 2017] [ssl:debug] [pid 1621:tid 139781198710528] ssl_engine_kernel.c(1812): [client 127.0.0.1:60678] AH02041: Protocol: TLSv1.2, Cipher: ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)
[Tue Mar 14 14:36:40.070935 2017] [ssl:debug] [pid 1621:tid 139781198710528] ssl_engine_kernel.c(224): [client 127.0.0.1:60678] AH02034: Initial (No.1) HTTPS request received for child 10 (server example.com:443)
[Tue Mar 14 14:36:45.076192 2017] [ssl:info] [pid 1621:tid 139781198710528] (70007)The timeout specified has expired: [client 127.0.0.1:60678] AH01991: SSL input filter read failed.
[Tue Mar 14 14:36:45.076234 2017] [ssl:debug] [pid 1621:tid 139781198710528] ssl_engine_io.c(992): [client 127.0.0.1:60678] AH02001: Connection closed to child 10 with standard shutdown (server example.com:443)

[Tue Mar 14 14:32:23.771725 2017] [ssl:info] [pid 1524:tid 140685759735552] [client 127.0.0.1:60658] AH01964: Connection to child 0 established (server example.com:443)
[Tue Mar 14 14:32:23.785078 2017] [ssl:debug] [pid 1524:tid 140685759735552] ssl_engine_kernel.c(1812): [client 127.0.0.1:60658] AH02041: Protocol: TLSv1.2, Cipher: ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)
[Tue Mar 14 14:32:33.795197 2017] [ssl:info] [pid 1524:tid 140685759735552] (70007)The timeout specified has expired: [client 127.0.0.1:60658] AH01991: SSL input filter read failed.
[Tue Mar 14 14:32:33.795329 2017] [ssl:debug] [pid 1524:tid 140685759735552] ssl_engine_io.c(992): [client 127.0.0.1:60658] AH02001: Connection closed to child 0 with standard shutdown (server example.com:443)