For me If snippet calls are failing to do anything other then return blank. I have found to places where it has failed once as a snippet and once as a custom output filter. Even when using &then &else neither show up.
I believe when using is as a filter there is no cache involved so that could not be the issue here.
The If filter that is failing can be tested if you have a copy of VC R4 running.
This fails (orderStep1/config.default.php)
Note: original code was using a lowercase "if" changed to uppercase but that did not resolve anything
[[!+orderAmountMet:If=`[[+orderAmountMet]]`:is=`0`:then=`<b>You have not met the minimum order amount.</b>`:else=`
<div id="vcBasketWrapper-nextStep">
<form action="[[+action]]" method="post">
<input type="submit" value="Next" />
</form>
</div>
`]]
Started immediately after 2.1.2 upgrade