FastCGI cache file has too long header

[Palvelin Postmaster]

Hi,

I run nginx/1.14.0 (Ubuntu 18.04) and PHP-FPM 7.2. I get such occasional (daily) errors about too long cache file headers:

2018/12/13 10:39:49 [crit] 1537#1537: *760972 cache file "/var/lib/nginx/fastcgi/mydomain-fi/d/be/7a11ac32c28dc9f8c3d7da12fe3d6bed" has too long header, client: XXX.XXX.XXX.XXX, server: mydomain.fi, request: "GET /kotitreeni/ HTTP/1.1", host: ”mydomain.fi"

Can someone offer any insight as to why this is happening, what I could do to prevent it or how I could further analyze the cause?

Here are a couple examples of headers from such cache files _after_ the error log entry (possibly redundant, but anyhow):

       Â(\                    √\    ’\    ¶á
  x
≥""a652b989092efd137f04e13cad4af4b3"                                                                                              Accept-Encoding                                                                                                                 ˜,	ñ#Õ∫3`˝„u»˝Zt    
KEY: httpsGETmydomain.fi/kotitreeni/

 

3 Content-Type:  text/html; charset=UTF-8
Last-Modified: Thu, 13 Dec 2018 08:39:31 GMT
Expires: Thu, 13 Dec 2018 09:39:31 GMT
Pragma: public
Cache-Control: max-age=3582, public
ETag: "a652b989092efd137f04e13cad4af4b3"
X-Powered-By: W3 Total Cache/0.9.7
Content-Encoding: gzip
Vary: Accept-Encoding


       {\                    ˚\    k
\    \‘†Ö  s
Æ""4fca3f56d337d2057ce73a6dd5712d80"                                                                                              Accept-Encoding                                                                                                                 ûíL∏±ÀÕ·p	ÙÎ(,f    
KEY: httpsGETmydomain.fi/ruoka/

 

3 Content-Type:  text/html; charset=UTF-8
Last-Modified: Thu, 13 Dec 2018 07:02:19 GMT
Expires: Thu, 13 Dec 2018 08:02:19 GMT
Pragma: public
Cache-Control: max-age=1696, public
ETag: "4fca3f56d337d2057ce73a6dd5712d80"
X-Powered-By: W3 Total Cache/0.9.7
Content-Encoding: gzip
Vary: Accept-Encoding