I thought about the ‘spanking’ approach, but I applied some scientific method, and inspected the reservoir.. It turns out if it isn’t in ‘flush’ then you will get the symptom of poor flow. In my case, a part had broken off, and wedged in the ‘trough’ that the reservoir inserts, thus stopping it from being fully inserted.
After removing the object wedged in the place where the reservoir is inserted.. it was flush again, fully inserted, and I got normal working flow.
Conclusion: It’s quite likely that the spanking approach could have resolved due to the cause above. But instead of spanking it, just check your reservoir is fully inserted! :)