In brine, things get a little more complicated. We don't know...

In brine, things get a little more complicated.
We don't know exactly which method is being used to determine Li concentration, however for methods such as AAS determination (for example) "calcium, iron and sodium can significantly depress the absorption signal on lithium in an air/acetylene flame" (source: https://link.springer.com/article/10.1007/s002160051412)

A high magnesium to lithium ratio can also throw a spanner in the works during Li extraction (though MGX Minerals and the PurLucid team seem to have found a way to rapidly remove Mg from the brine)

It would be good to get specific details from Anson regarding the issues causing this delay, but my guess is that measuring Li concentration in the "metallic ion soup" they extracted simply turned out to be a more difficult and time consuming process than originally envisaged.