Weird SSL problems with RXS calls for a specific user

One of our customers uses Krengeltech RXS to communicate with web services from a program tied to an exit hook in one of our products.

For most users, this works reasonably well. But for a single specific user, it fails with a message to the effect of

RXS0000010 . . . RXS_getUri . . . SSL connect error

in the joblog.

On the advice of Krengeltech technical support, which sent me this link,
<https://isupport.krengeltech.com/rxs/configuring_ssl_permissions/>
I checked the permissions of /QIBM/UserData/ICSS/Cert/Server. The files in the directory are already both *PUBLIC *R, and all the directories in the path are already *PUBLIC *RX all the way down to /QIBM.

Anybody got any ideas what could be going on? I've already sent Krengeltech my findings.

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JHHL