Sub-floor air flow is often insufficient. Consider increasing sub-floor ventilation, either with more airbricks or an inline extractor such as this; https://www.amazon.co.uk/gp/product/B07KRWXW8W/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1. With rigid
Sub-floor extractor fan. Consider installing a sub-floor fan. It is imperative that access is easy, usage controlled and sub-floor humidity is monitored. These can be done remotely, see surveyor.tips/sub-floor-fan.
Rain bouncing into sub-floor vents. Consider lowering the ground under the sub-floor vents to stop rain bouncing in. I don’t it is necessary, but the gold standard is installing an Aco drain, discharging into the drainage system (the cost of that would be