一台服务器上使用包含多个顶级域名的 SAN 证书，但 nginx 只返回其中一个的网页内容

现有 2 个顶级域名（ a.com,b.com ），都包含在证书的 SAN 扩展里。在 nginx 里也分别有配置两个顶级域名的对应文件目录。问题是，无论访问 a.com 还是 b.com ，nginx 只会返回作为证书 Common Name 的那个域名对应的网站内容，而剩下的那个域名的配置似乎自动被 nginx 忽略了。

nginx 版本是 1.13.3，支持 SNI，静态编译的 OpenSSL 版本为 1.0.2k ，通过 nginx-ct 模块开启了 certificate transparency 策略。

请问有可能是哪些方面的原因？谢谢！ 配置如下： a.com(common name):

server {
    server_name a.com www.a.com;

    location ^~ /.well-known/acme-challenge/ {
        alias /home/check/;
        try_files $uri =404;
    }

    location / {
        rewrite ^/(.*)$ https://a.com/$1 permanent;
    }
}
server {
    server_name a.com www.a.com;
    listen               443 ssl http2;
    root /home/wwwroot/a;
    server_tokens        off;
    ssl_ct on;
    ssl_certificate      /root/ssl/double.rsa.pem;
    ssl_certificate_key  /root/ssl/double.rsa.key;
    ssl_ct_static_scts   /root/ssl/scts/rsa;

    ssl_certificate      /root/ssl/double.ecc.pem;
    ssl_certificate_key  /root/ssl/double.ecc.key;
    ssl_ct_static_scts   /root/ssl/scts/ecc;
    ssl_dhparam          /root/ssl/dhparams.pem;
    ssl_ciphers EECDH+ECDSA+AES128:EECDH+aRSA+AES128:RSA+AES128:EECDH+ECDSA+AES256:EECDH+aRSA+AES256:RSA+AES256:EECDH+ECDSA+3DES:EECDH+aRSA+3DES:RSA+3DES:!MD5;
    ssl_prefer_server_ciphers  on;
    ssl_ecdh_curve secp384r1;
    ssl_protocols              TLSv1 TLSv1.1 TLSv1.2;
    ssl_session_cache          shared:SSL:50m;
    ssl_session_timeout        1d;
    ssl_session_tickets        on;
    ssl_stapling               on;
    ssl_stapling_verify        on;
    resolver                   8.8.8.8 8.8.4.4 valid=300s;
    resolver_timeout           10s;
    add_header    Strict-Transport-Security 'max-age=31536000; includeSubDomains; preload';
    add_header    Public-Key-Pins 'pin-sha256="YLh1dUR9y6Kja30RrAn7JKnbQG/uEtLMkBgFF2Fuihg=";pin-sha256="Fbs+o+IxVNTHBpjNQYfX/TBnxPC+OWLYxQLEtqkrAfM=";max-age=2592000; includeSubDomains';
    index index.html;
    location / {
        expires 120s;
    }
    location ~ .*\.(gif|jpg|jpeg|png|bmp|swf|flv|ico)$ {
    expires 30d;
    access_log off;
    }
location ~ .*\.(js|css)?$ {
    expires 7d;
    access_log off;
    }
}

b.com:

server {
    server_name b.com www.b.com;

    location ^~ /.well-known/acme-challenge/ {
        alias /home/check/;
        try_files $uri =404;
    }

    location / {
        rewrite ^/(.*)$ https://b.com/$1 permanent;
    }
}
server {
    server_name b.com www.b.com;
    listen               443 ssl http2;
    index index.php;
    root  /home/wwwroot/b;

    if (!-e $request_filename) {
        rewrite ^(.*)$ /index.php$1 last;
    }

    location ~ .*\.php(\/.*)*$ {
                include fastcgi.conf;
                fastcgi_pass  cgi:9001;
    }

    server_tokens        off;
    ssl_ct on;
    ssl_certificate      /root/ssl/double.rsa.pem;
    ssl_certificate_key  /root/ssl/double.rsa.key;
    ssl_ct_static_scts   /root/ssl/scts/rsa;

    ssl_certificate      /root/ssl/double.ecc.pem;
    ssl_certificate_key  /root/ssl/double.ecc.key;
    ssl_ct_static_scts   /root/ssl/scts/ecc;
    ssl_dhparam          /root/ssl/dhparams.pem;
    ssl_ciphers EECDH+ECDSA+AES128:EECDH+aRSA+AES128:RSA+AES128:EECDH+ECDSA+AES256:EECDH+aRSA+AES256:RSA+AES256:EECDH+ECDSA+3DES:EECDH+aRSA+3DES:RSA+3DES:!MD5;
    ssl_prefer_server_ciphers  on;
    ssl_ecdh_curve secp384r1;
    ssl_protocols              TLSv1 TLSv1.1 TLSv1.2;
    ssl_session_cache          shared:SSL:50m;
    ssl_session_timeout        1d;
    ssl_session_tickets        on;
    ssl_stapling               on;
    ssl_stapling_verify        on;
    resolver                   8.8.8.8 8.8.4.4 valid=300s;
    resolver_timeout           10s;
    add_header    Strict-Transport-Security 'max-age=31536000; includeSubDomains; preload';
    add_header    Public-Key-Pins 'pin-sha256="YLh1dUR9y6Kja30RrAn7JKnbQG/uEtLMkBgFF2Fuihg=";pin-sha256="Fbs+o+IxVNTHBpjNQYfX/TBnxPC+OWLYxQLEtqkrAfM=";max-age=2592000; includeSubDomains';
}

error_log  /root/b_error.log  crit;