A Material Valuation Uncertainty declaration is applicable when there are sharp and unpredicted shocks to a market leading to a temporary suspension of market activity. The RICS recommended their use on 17th March 2020 and they were only expected to be applicable for a relatively short term.
For properties where there is little transactional comparable evidence, other indicators should be considered.
As I have noted in previous updates on this subject, it is still down to the valuer to consider each property individually and for some properties the valuer might still believe it is appropriate to include a Material Valuation Uncertainty clause.