So essentially OLCI does work for you and you manage to print your BPs however the procedures are slightly different for Changi. It's not a website failure which OP is asking about.
Quote from FAQs from the SQ website...
Please be aware that if you hold a mobile boarding pass and are departing from Singapore, you would either be re-issued with a traditional boarding pass when you drop-off your bags or a receipt by airport security prior to immigration. This is a Changi airport authority requirement, for security and immigration purposes.
You may also be re-issued with a traditional boarding pass if there is a seat change, which could be requested by you or due to operational issues such as aircraft change or other exigencies.
That's why I never print my BPs anyway, since I'm going to have to stop by the counters to drop off my bags or get my documents verified.