Sadly it doesnt help

src/calibre/srv/loop.py

@@ -648,16 +648,8 @@ def write_to_control(self, what):
         if iswindows:
             self.control_in.sendall(what)
         else:
-            try:
-                self.control_in.write(what)
-                self.control_in.flush()
-            except BrokenPipeError:
-                # this started happening in the CI environment for the ajax_book test
-                # in early Dec 2020
-                self.log.error('Control pipe broken, resetting')
-                self.create_control_connection()
-                self.control_in.write(what)
-                self.control_in.flush()
+            self.control_in.write(what)
+            self.control_in.flush()
 
     def wakeup(self):
         self.write_to_control(WAKEUP)

src/calibre/srv/tests/ajax.py

@@ -7,7 +7,6 @@
 
 import json
 import os
-import time
 import zlib
 from functools import partial
 from io import BytesIO
@@ -38,12 +37,7 @@ def test_ajax_book(self):  # {{{
             db = server.handler.router.ctx.library_broker.get(None)
             conn = server.connect()
             request = partial(make_request, conn, prefix='/ajax/book')
-
-            try:
-                r, data = request('/x')
-            except ConnectionRefusedError:
-                time.sleep(2)
-                r, data = request('/x')
+            r, data = request('/x')
             self.ae(r.status, NOT_FOUND)
 
             r, onedata = request('/1')