Why did my Pushover integration stopp working all of a sudden?

Problem:

It’s been working somewhat well for 2 almost years but now it stopped working altogether, meaning I can’t use it to send messages to my devices via HA. I believe the error occurred after I changed my router. At first it produced this error in the HA logs:

Logger: homeassistant.config_entries
Source: config_entries.py:586
First occurred: January 23, 2025 at 15:50:02 (1 occurrences)
Last logged: January 23, 2025 at 15:50:02

Error setting up entry Pushover for pushover
Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/urllib3/connectionpool.py", line 715, in urlopen
    httplib_response = self._make_request(
                       ^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/urllib3/connectionpool.py", line 404, in _make_request
    self._validate_conn(conn)
  File "/usr/local/lib/python3.12/site-packages/urllib3/connectionpool.py", line 1060, in _validate_conn
    conn.connect()
  File "/usr/local/lib/python3.12/site-packages/urllib3/connection.py", line 419, in connect
    self.sock = ssl_wrap_socket(
                ^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/urllib3/util/ssl_.py", line 449, in ssl_wrap_socket
    ssl_sock = _ssl_wrap_socket_impl(
               ^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/urllib3/util/ssl_.py", line 493, in _ssl_wrap_socket_impl
    return ssl_context.wrap_socket(sock, server_hostname=server_hostname)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/ssl.py", line 455, in wrap_socket
    return self.sslsocket_class._create(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/ssl.py", line 1042, in _create
    self.do_handshake()
  File "/usr/local/lib/python3.12/ssl.py", line 1320, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLCertVerificationError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: self-signed certificate (_ssl.c:1000)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/requests/adapters.py", line 667, in send
    resp = conn.urlopen(
           ^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/urllib3/connectionpool.py", line 801, in urlopen
    retries = retries.increment(
              ^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/urllib3/util/retry.py", line 594, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='api.pushover.net', port=443): Max retries exceeded with url: /1/users/validate.json (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: self-signed certificate (_ssl.c:1000)')))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/config_entries.py", line 586, in async_setup
    result = await component.async_setup_entry(hass, self)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/components/pushover/__init__.py", line 37, in async_setup_entry
    await hass.async_add_executor_job(
  File "/usr/local/lib/python3.12/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/pushover_complete/pushover_api.py", line 239, in validate
    return self._generic_post('users/validate.json', payload=payload)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/pushover_complete/pushover_api.py", line 81, in _generic_post
    resp = post(
           ^^^^^
  File "/usr/local/lib/python3.12/site-packages/requests/api.py", line 115, in post
    return request("post", url, data=data, json=json, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/requests/api.py", line 59, in request
    return session.request(method=method, url=url, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/requests/sessions.py", line 589, in request
    resp = self.send(prep, **send_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/requests/sessions.py", line 703, in send
    r = adapter.send(request, **kwargs)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/requests/adapters.py", line 698, in send
    raise SSLError(e, request=request)
requests.exceptions.SSLError: HTTPSConnectionPool(host='api.pushover.net', port=443): Max retries exceeded with url: /1/users/validate.json (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: self-signed certificate (_ssl.c:1000)')))

Then, after a reboot and after I changed my user keys it says “Failed Setup, will retry: 400: user key is invalid” on the integration page.
When I try to enter the new key via Add Entry and then entering it it produces an error that goes something like “Error: Intergration already set up”

Solution:
So what I had to do was actually delete my previous Pushover entry and then add a new one and now it’s working again.

Question:
Why did it happen in the first place? I don’t see the correlation between this issue and me changing my router.