I agree with the algae issue due to water contamination. Since your bus is still running, I’d recommend taking it on a 100-mile trip and then changing all the filters again. The filters have likely done their best to catch the contaminants, and fuel starvation can occur once they’re clogged.
Regarding Racor vacuum gauges, they’re not ideal for highway applications because they can be exposed to flying debris and vibration. Marine applications are better suited for these gauges due to the enclosed engine rooms that offer protection.
Using an algaecide additive is crucial in your case. Follow the directions for a double dose on the first treatment. Although it’s a bit pricey (around $20 or more), it’s much more economical than a full fuel polishing treatment.