Intermittent TLS SecureChannelFailure with client certificates

Question

I have an F5 load-balanced API which calls out to external API's, some of which require mutual ("two way" / client) SSL.

For months things work fine, but from time-to-time requests (to the external APIs) fail with a "SecureChannelFailure : The request was aborted: Could not create SSL/TLS secure channel".

What's interesting is the same error is reported for requests made to API's which do not require mutual SSL.

An IIS app-pool recycle (for my API) resolves the issue.

While researching possible causes for this I've come across vague mention that this type of intermittent issue may be caused by the F5... but, unfortunately, no more information is mentioned.

Answer 1

IT tracked this down to a box with the incorrect permissions set for the relevant certificate. It seems the issue only manifested periodically when loaded shifted to this box.