DICOM TLS between Orthanc and pynetDicom fails with error ErrorDetails: DicomAssociation - connecting to AET "MY_AET": TLS error: OpenSSL error

Question

I am trying to create a secure communication between Orthanc(client on my local (Mac)) and pynetDicom(server on my EC2). For this I obtained X.509 certificate from Lets Encrypt. I have added the certs to pynetDicom like this in the pythons ssl context

# Set up TLS
context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
context.load_cert_chain(certfile=CERT_FILE, keyfile=KEY_FILE, password=None)

# If a certificate chain file is needed
context.load_verify_locations(cafile=CHAIN_FILE)

ae.tls_server_context = context

assoc = ae.start_server(
    (NODE_IP, NODE_PORT),
    ae_title=AE_TITLE,
    evt_handlers=handlers,
    ssl_context=ae.tls_server_context  # Enable TLS
)

I tried testing the TLS connection with openssl and it works with -partialChain tag, with an error at the end: openssl s_client -connect pacs.avendahealth.com:443 -CAfile /Users/sumitjanawlekar/pynetDicom_cert/fullchain.pem -partial_chain with

 Start Time: 1695710162
    Timeout   : 7200 (sec)
    Verify return code: 0 (ok)
    Extended master secret: no
---
80208DF401000000:error:0A000126:SSL routines:ssl3_read_n:unexpected eof while reading:ssl/record/rec_layer_s3.c:304:

Without the partialChain tag it fails with error

Start Time: 1695710953
    Timeout   : 7200 (sec)
    Verify return code: 2 (unable to get issuer certificate)
    Extended master secret: no
---
80208DF401000000:error:0A000126:SSL routines:ssl3_read_n:unexpected eof while reading:ssl/record/rec_layer_s3.c:304:

When I try sending Dicom data from Orthanc, it fails with this reason.

ErrorCode: 9
ErrorDescription: Error in the network protocol
ErrorDetails: DicomAssociation - connecting to AET "MY_AET": TLS error: OpenSSL error

I am new to this, how can I make this work?

PSA: the connection works fine as I turn off TLS. Also the request flows like this DICOM Client -> aws network load balancer (NLB) -> Ec2(pynetDicom running here). I even tried terminating TLS at the NLB level, still same error

I have tried TLS termination, encryption at pynetDicom level, I even tried local setup (client and server both as Orthanc running on local), testing with tools like openssl etc. All did not work.