The expansion of the log macros can double-evaluate the first argument.

For example, the following call:

(log/info (expensive-call foo) bar)

Expands to this:

(let*
[logger_278auto_
(get-logger logger-factory #<Namespace scratch.core>)]
(if (enabled? logger_278auto_ :info)
(if (instance? java.lang.Throwable (expensive-call foo))
(log*
logger_278auto_
:info
(expensive-call foo)
(print-str bar))
(log*
logger_278auto_
:info
nil
(print-str (expensive-call foo) bar)))))

Note the calls to "expensive-call" both in the instance check and in the log* call.