The FTX trade happened in April 2021 and it looks like it was because the value of mobilecoin spiked and someone in FTX bet on it at a high price before it dropped.
I don’t think this was some FTX investment directly to mobilecoin itself (they were buying coins, not loans/investment that would expose them to FTXs recent drop). Despite the headline making it seem that way. In the year plus since the Apr 2021 price spike mobilecoin price is pretty stable.
So I’m not sure why Signal should drop them other than because of the general volatility in crypto.