Instrumentlal rationality and epistemic rationality aren’t the same. Epistemic rationality seeks to maxmise knowledge, truth and consistency. Instrumental rationality seeks to maximise efficiemcy, gain and personal utility.One area they come apart is signalling, the implicit and explicit ways we tell others what kind of person we are. The instrumentally rational way is to signal is to maximise your utility by sending out agreeable signals to whichever individual or group youhappen to need something from. This Vicar-of-Bray style behaviour will lead to your making highly inconsistent statements in the limit. If you want to signal sincerity, you will need to believe them too.So you will end up with inconsistent beliefs. So,IR+signalling is inconsistent with ER.