Error after upgrading to version 13. New Sales Order page becomes unresponsive

Hi,
I have recently upgraded a server from version 11 to version 13 by import database.
All of a sudden new sales order form started going unresponsive.
Following is the error log from
node-socketio.log

{ Error: Not Found
at Request.callback (/home/frappe/frappe-bench/apps/frappe/node_modules/superagent/lib/node/index.js:706:15)
at parser (/home/frappe/frappe-bench/apps/frappe/node_modules/superagent/lib/node/index.js:916:18)
at IncomingMessage.res.on (/home/frappe/frappe-bench/apps/frappe/node_modules/superagent/lib/node/parsers/json.js:19:7)
at emitNone (events.js:111:20)
at IncomingMessage.emit (events.js:208:7)
at endReadableNT (_stream_readable.js:1064:12)
at _combinedTickCallback (internal/process/next_tick.js:139:11)
at process._tickCallback (internal/process/next_tick.js:181:9)
status: 404,
response:
Response {
domain: null,
_events: {},
_eventsCount: 0,
_maxListeners: undefined,
res:
IncomingMessage {
_readableState: [Object],
readable: false,
domain: null,
_events: [Object],
_eventsCount: 4,
_maxListeners: undefined,
socket: [Object],
connection: [Object],
httpVersionMajor: 1,
httpVersionMinor: 1,
httpVersion: ‘1.1’,
complete: true,
headers: [Object],
rawHeaders: [Array],
trailers: {},
rawTrailers: [],
aborted: false,
upgrade: false,
url: ‘’,
method: null,
statusCode: 404,
statusMessage: ‘NOT FOUND’,
client: [Object],
_consuming: true,
_dumped: false,
req: [Object],
text: ‘{“exc_type”:“DoesNotExistError”,“_server_messages”:“[\”{\\\“message\\\”: \\\“Sales Order New Sales Order 1 not found\\\”, \\\“indicator\\\”: \\\“red\\\”, \\\“raise_exception\\\”: 1}\“]”}’,
read: [Function] },
request:
Request {
domain: null,
_events: {},
_eventsCount: 0,
_maxListeners: undefined,
_agent: false,
_formData: null,
method: ‘GET’,
url: ‘http://164.92.193.171/api/method/frappe.realtime.can_subscribe_doc?sid=29cbad20eaf1a74a4990b6ab1c8c7cf3223468fbc43f9af75d6964cc&doctype=Sales%20Order&docname=New%20Sales%20Order%201’,
_header: [Object],
header: [Object],
writable: true,
_redirects: 0,
_maxRedirects: 5,
cookies: ‘’,
qs: {},
_query: [],
qsRaw: [],
_redirectList: [],
_streamRequest: false,
req: [Object],
protocol: ‘http:’,
host: ‘164.92.193.171’,
_endCalled: true,
_callback: [Function],
res: [Object],
response: [Circular],
called: true },
req:
ClientRequest {
domain: null,
_events: [Object],
_eventsCount: 3,
_maxListeners: undefined,
output: [],
outputEncodings: [],
outputCallbacks: [],
outputSize: 0,
writable: true,
_last: true,
upgrading: false,
chunkedEncoding: false,
shouldKeepAlive: false,
useChunkedEncodingByDefault: false,
sendDate: false,
_removedConnection: false,
_removedContLen: false,
_removedTE: false,
_contentLength: 0,
_hasBody: true,
_trailer: ‘’,
finished: true,
_headerSent: true,
socket: [Object],
connection: [Object],
_header: ‘GET /api/method/frappe.realtime.can_subscribe_doc?sid=29cbad20eaf1a74a4990b6ab1c8c7cf3223468fbc43f9af75d6964cc&doctype=Sales%20Order&docname=New%20Sales%20Order%201 HTTP/1.1\r\nHost: 164.92.193.171\r\nAccept-Encoding: gzip, deflate\r\nUser-Agent: node-superagent/3.8.3\r\nContent-Type: application/x-www-form-urlencoded\r\nConnection: close\r\n\r\n’,
_onPendingData: [Function: noopPendingOutput],
agent: [Object],
socketPath: undefined,
timeout: undefined,
method: ‘GET’,
path: ‘/api/method/frappe.realtime.can_subscribe_doc?sid=29cbad20eaf1a74a4990b6ab1c8c7cf3223468fbc43f9af75d6964cc&doctype=Sales%20Order&docname=New%20Sales%20Order%201’,
_ended: true,
res: [Object],
aborted: undefined,
timeoutCb: null,
upgradeOrConnect: false,
parser: null,
maxHeadersCount: null,
[Symbol(outHeadersKey)]: [Object] },
text: ‘{“exc_type”:“DoesNotExistError”,“_server_messages”:“[\”{\\\“message\\\”: \\\“Sales Order New Sales Order 1 not found\\\”, \\\“indicator\\\”: \\\“red\\\”, \\\“raise_exception\\\”: 1}\“]”}’,
body:
{ exc_type: ‘DoesNotExistError’,
_server_messages: ‘[“{\“message\”: \“Sales Order New Sales Order 1 not found\”, \“indicator\”: \“red\”, \“raise_exception\”: 1}”]’ },
files: undefined,
buffered: true,
headers:
{ server: ‘nginx’,
date: ‘Thu, 10 Mar 2022 06:54:08 GMT’,
‘content-type’: ‘application/json’,
‘content-length’: ‘186’,
connection: ‘close’,
‘set-cookie’: [Array] },
header:
{ server: ‘nginx’,
date: ‘Thu, 10 Mar 2022 06:54:08 GMT’,
‘content-type’: ‘application/json’,
‘content-length’: ‘186’,
connection: ‘close’,
‘set-cookie’: [Array] },
statusCode: 404,
status: 404,
statusType: 4,
info: false,
ok: false,
redirect: false,
clientError: true,
serverError: false,
error:
{ Error: cannot GET /api/method/frappe.realtime.can_subscribe_doc?sid=29cbad20eaf1a74a4990b6ab1c8c7cf3223468fbc43f9af75d6964cc&doctype=Sales%20Order&docname=New%20Sales%20Order%201 (404)
at Response.toError (/home/frappe/frappe-bench/apps/frappe/node_modules/superagent/lib/node/response.js:94:15)
at ResponseBase._setStatusProperties (/home/frappe/frappe-bench/apps/frappe/node_modules/superagent/lib/response-base.js:123:16)
at new Response (/home/frappe/frappe-bench/apps/frappe/node_modules/superagent/lib/node/response.js:41:8)
at Request._emitResponse (/home/frappe/frappe-bench/apps/frappe/node_modules/superagent/lib/node/index.js:752:20)
at parser (/home/frappe/frappe-bench/apps/frappe/node_modules/superagent/lib/node/index.js:916:38)
at IncomingMessage.res.on (/home/frappe/frappe-bench/apps/frappe/node_modules/superagent/lib/node/parsers/json.js:19:7)
at emitNone (events.js:111:20)
at IncomingMessage.emit (events.js:208:7)
at endReadableNT (_stream_readable.js:1064:12)
at _combinedTickCallback (internal/process/next_tick.js:139:11)
status: 404,
text: ‘{“exc_type”:“DoesNotExistError”,“_server_messages”:“[\”{\\\“message\\\”: \\\“Sales Order New Sales Order 1 not found\\\”, \\\“indicator\\\”: \\\“red\\\”, \\\“raise_exception\\\”: 1}\“]”}’,
method: ‘GET’,
path: ‘/api/method/frappe.realtime.can_subscribe_doc?sid=29cbad20eaf1a74a4990b6ab1c8c7cf3223468fbc43f9af75d6964cc&doctype=Sales%20Order&docname=New%20Sales%20Order%201’ },
created: false,
accepted: false,
noContent: false,
badRequest: false,
unauthorized: false,
notAcceptable: false,
forbidden: false,
notFound: true,
unprocessableEntity: false,
type: ‘application/json’,
links: {},
setEncoding: [Function: bound ],
redirects: [] } }

Any help is appreciated.

Don’t take leap,

First upgrade version-11 to version-12,
then upgrade version-12 to version-13

That’s all!

Have followed the same path

Got the error
It was due to letter head fetch from field