This is what is in the debug logs:
time="2021-03-18T12:04:14Z" level=debug msg="Serving default certificate for request: \"domain.com\""
time="2021-03-18T12:04:14Z" level=debug msg="http: TLS handshake error from 192.168.5.13:57001: remote error: tls: unknown certificate"
time="2021-03-18T12:04:14Z" level=debug msg="Serving default certificate for request: \"domain.com\""
time="2021-03-18T12:04:14Z" level=debug msg="vulcand/oxy/roundrobin/rr: begin ServeHttp on request" Request="{\"Method\":\"GET\",\"URL\":{\"Scheme\":\"\",\"Opaque\":\"\",\"User\":null,\"Host\":\"\",\"Path\":\"/\",\"RawPath\":\"\",\"ForceQuery\":false,\"RawQuery\":\"\",\"Fragment\":\"\",\"RawFragment\":\"\"},\"Proto\":\"HTTP/2.0\",\"ProtoMajor\":2,\"ProtoMinor\":0,\"Header\":{\"Accept\":[\"text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9\"],\"Accept-Encoding\":[\"gzip, deflate, br\"],\"Accept-Language\":[\"en-GB,en;q=0.9\"],\"Sec-Ch-Ua\":[\"\\\"Google Chrome\\\";v=\\\"89\\\", \\\"Chromium\\\";v=\\\"89\\\", \\\";Not A Brand\\\";v=\\\"99\\\"\"],\"Sec-Ch-Ua-Mobile\":[\"?0\"],\"Sec-Fetch-Dest\":[\"document\"],\"Sec-Fetch-Mode\":[\"navigate\"],\"Sec-Fetch-Site\":[\"none\"],\"Sec-Fetch-User\":[\"?1\"],\"Upgrade-Insecure-Requests\":[\"1\"],\"User-Agent\":[\"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.82 Safari/537.36\"],\"X-Forwarded-Host\":[\"domain.com\"],\"X-Forwarded-Port\":[\"443\"],\"X-Forwarded-Proto\":[\"https\"],\"X-Forwarded-Server\":[\"traefik-external-b677dc764-867sj\"],\"X-Real-Ip\":[\"192.168.5.13\"]},\"ContentLength\":0,\"TransferEncoding\":null,\"Host\":\"domain.com\",\"Form\":null,\"PostForm\":null,\"MultipartForm\":null,\"Trailer\":null,\"RemoteAddr\":\"192.168.5.13:64137\",\"RequestURI\":\"/\",\"TLS\":null}"
time="2021-03-18T12:04:14Z" level=debug msg="vulcand/oxy/roundrobin/rr: Forwarding this request to URL" Request="{\"Method\":\"GET\",\"URL\":{\"Scheme\":\"\",\"Opaque\":\"\",\"User\":null,\"Host\":\"\",\"Path\":\"/\",\"RawPath\":\"\",\"ForceQuery\":false,\"RawQuery\":\"\",\"Fragment\":\"\",\"RawFragment\":\"\"},\"Proto\":\"HTTP/2.0\",\"ProtoMajor\":2,\"ProtoMinor\":0,\"Header\":{\"Accept\":[\"text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9\"],\"Accept-Encoding\":[\"gzip, deflate, br\"],\"Accept-Language\":[\"en-GB,en;q=0.9\"],\"Sec-Ch-Ua\":[\"\\\"Google Chrome\\\";v=\\\"89\\\", \\\"Chromium\\\";v=\\\"89\\\", \\\";Not A Brand\\\";v=\\\"99\\\"\"],\"Sec-Ch-Ua-Mobile\":[\"?0\"],\"Sec-Fetch-Dest\":[\"document\"],\"Sec-Fetch-Mode\":[\"navigate\"],\"Sec-Fetch-Site\":[\"none\"],\"Sec-Fetch-User\":[\"?1\"],\"Upgrade-Insecure-Requests\":[\"1\"],\"User-Agent\":[\"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.82 Safari/537.36\"],\"X-Forwarded-Host\":[\"domain.com\"],\"X-Forwarded-Port\":[\"443\"],\"X-Forwarded-Proto\":[\"https\"],\"X-Forwarded-Server\":[\"traefik-external-b677dc764-867sj\"],\"X-Real-Ip\":[\"192.168.5.13\"]},\"ContentLength\":0,\"TransferEncoding\":null,\"Host\":\"domain.com\",\"Form\":null,\"PostForm\":null,\"MultipartForm\":null,\"Trailer\":null,\"RemoteAddr\":\"192.168.5.13:64137\",\"RequestURI\":\"/\",\"TLS\":null}" ForwardURL="http://10.42.3.75:80"
time="2021-03-18T12:04:14Z" level=debug msg="vulcand/oxy/roundrobin/rr: completed ServeHttp on request" Request="{\"Method\":\"GET\",\"URL\":{\"Scheme\":\"\",\"Opaque\":\"\",\"User\":null,\"Host\":\"\",\"Path\":\"/\",\"RawPath\":\"\",\"ForceQuery\":false,\"RawQuery\":\"\",\"Fragment\":\"\",\"RawFragment\":\"\"},\"Proto\":\"HTTP/2.0\",\"ProtoMajor\":2,\"ProtoMinor\":0,\"Header\":{\"Accept\":[\"text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9\"],\"Accept-Encoding\":[\"gzip, deflate, br\"],\"Accept-Language\":[\"en-GB,en;q=0.9\"],\"Sec-Ch-Ua\":[\"\\\"Google Chrome\\\";v=\\\"89\\\", \\\"Chromium\\\";v=\\\"89\\\", \\\";Not A Brand\\\";v=\\\"99\\\"\"],\"Sec-Ch-Ua-Mobile\":[\"?0\"],\"Sec-Fetch-Dest\":[\"document\"],\"Sec-Fetch-Mode\":[\"navigate\"],\"Sec-Fetch-Site\":[\"none\"],\"Sec-Fetch-User\":[\"?1\"],\"Upgrade-Insecure-Requests\":[\"1\"],\"User-Agent\":[\"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.82 Safari/537.36\"],\"X-Forwarded-Host\":[\"domain.com\"],\"X-Forwarded-Port\":[\"443\"],\"X-Forwarded-Proto\":[\"https\"],\"X-Forwarded-Server\":[\"traefik-external-b677dc764-867sj\"],\"X-Real-Ip\":[\"192.168.5.13\"]},\"ContentLength\":0,\"TransferEncoding\":null,\"Host\":\"domain.com\",\"Form\":null,\"PostForm\":null,\"MultipartForm\":null,\"Trailer\":null,\"RemoteAddr\":\"192.168.5.13:64137\",\"RequestURI\":\"/\",\"TLS\":null}"