Hey, did you manage to solve it somehow?
Today I had the same issue:

First, an error about "ignore long locked inactive cache":
2022/01/06 16:25:57 [alert] 1851#1851: ignore long locked inactive cache entry 296f4c8a7a86be9ab8b0b1f7a36a24c9, count:1
2022/01/06 16:25:57 [alert] 1851#1851: ignore long locked inactive cache entry b7955e11728bc786ee1f3dfe4431ed46, count:1
2022/01/06 16:26:00 [alert] 1851#1851: ignore long locked inactive cache entry 994c71d9331e2ce359343c5a0585cc12, count:1
2022/01/06 16:26:45 [alert] 1851#1851: ignore long locked inactive cache entry 257227d10b2e8313fe28ae26e54c26bf, count:1
2022/01/06 16:26:45 [alert] 1851#1851: ignore long locked inactive cache entry 464329e85103586eb975860f942d2e01, count:1
2022/01/06 16:26:46 [alert] 1851#1851: ignore long locked inactive cache entry 77b4d4013a0462ba32073c9ae8b17b3f, count:2
...
2022/01/06 16:32:21 [alert] 1851#1851: ignore long locked inactive cache entry c423a4bc3ff5e1938e6e3feaaa97bd26, count:6
2022/01/06 16:32:21 [alert] 1851#1851: ignore long locked inactive cache entry fa16439b534bc481f0c165d98650e306, count:6
2022/01/06 16:32:29 [alert] 1851#1851: ignore long locked inactive cache entry 61faee7679ad426fdc296b6f14915ef4, count:2
2022/01/06 16:32:29 [alert] 1851#1851: ignore long locked inactive cache entry ff1bd077430d4b87c1c1424c3746d850, count:2

Then, an error about "too many open files":
2022/01/06 16:32:30 [crit] 1816#1816: accept4() failed (24: Too many open files)
2022/01/06 16:32:31 [crit] 1816#1816: accept4() failed (24: Too many open files)
2022/01/06 16:32:31 [crit] 1816#1816: accept4() failed (24: Too many open files)
2022/01/06 16:32:32 [crit] 1816#1816: accept4() failed (24: Too many open files)
2022/01/06 16:32:32 [crit] 1816#1816: accept4() failed (24: Too many open files)
2022/01/06 16:32:33 [crit] 1816#1816: accept4() failed (24: Too many open files)

Here's my nginx -V output:
root@my-precious-server# nginx -V
nginx version: nginx/1.14.0 (Ubuntu)
built with OpenSSL 1.1.1 11 Sep 2018
TLS SNI support enabled
configure arguments: --with-cc-opt='-g -O2 -fdebug-prefix-map=/build/nginx-H4cN7P/nginx-1.14.0=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -Wdate-time -D_FORTIFY_SOURCE=2' --with-ld-opt='-Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fPIC' --prefix=/usr/share/nginx --conf-path=/etc/nginx/nginx.conf --http-log-path=/var/log/nginx/access.log --error-log-path=/var/log/nginx/error.log --lock-path=/var/lock/nginx.lock --pid-path=/run/nginx.pid --modules-path=/usr/lib/nginx/modules --http-client-body-temp-path=/var/lib/nginx/body --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-proxy-temp-path=/var/lib/nginx/proxy --http-scgi-temp-path=/var/lib/nginx/scgi --http-uwsgi-temp-path=/var/lib/nginx/uwsgi --with-debug --with-pcre-jit --with-http_ssl_module --with-http_stub_status_module --with-http_realip_module --with-http_auth_request_module --with-http_v2_module --with-http_dav_module --with-http_slice_module --with-threads --with-http_addition_module --with-http_geoip_module=dynamic --with-http_gunzip_module --with-http_gzip_static_module --with-http_image_filter_module=dynamic --with-http_sub_module --with-http_xslt_module=dynamic --with-stream=dynamic --with-stream_ssl_module --with-mail=dynamic --with-mail_ssl_module

What I did was to restart the php-fpm service, and than it worked....but this is just a work-around :(