SSLError during Robot Framework tests - ssl

Question

I have a problem with RF tests. I have built tests with TLS and certificates using "Create Client Cert Session" keywords. I have a specific keywords to do this:
Start Session
Log Creating HTTPS Session
#{client_certs}= Create List ${CERT} ${PRIVKEY}
Create Client Cert Session ${SESSION} ${HOST} client_certs=#{client_certs} verify=${CA} debug=1 timeout=20 disable_warnings=1
Log HTTPS Session has been created!
where ${CERT} and ${PRIVKEY} are respectively the certificate and the private key paths, ${SESSION} is the alias, ${HOST} is the hostname and ${CA} is the certificate authority. I execute this keyword as suite initialization.
This is an example of test:
Test
&{headers}= Create Dictionary &{contentTypeDict}
${response}= Get Request ${SESSION} ${BASEURL}/${endPoint} headers=${headers}
Status Should Be ${expectedResponse} ${response}
When this test is performed, Robot Framework raises the following error:
Test 'Test' failed after retrying for 30 seconds. The last error was: SSLError:
HTTPSConnectionPool(host='myhostname', port=8080): Max retries exceeded with url: /url/to/resource
(Caused by SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:852)'),))
This problem doesn't always happen, but sometimes tests are successful and sometimes they fail. What could be the problem? Certificates are correct and have not expired (I check them before executing tests).