fix VAIMAcc in gibbs/MH

Author: penelopeysm

src/mcmc/gibbs.jl

@@ -464,7 +464,12 @@ function setparams_varinfo!!(
     model::DynamicPPL.Model, ::MH, state::AbstractVarInfo, params::AbstractVarInfo
 )
     # Setting `params` into `state` really just means using `params` itself, but we
-    # need to update the logprob.
+    # need to update the logprob. We also need to be a bit more careful, because
+    # the `state` here carries a VAIMAcc, which is needed for the MH step() function
+    # but may not be present in `params`. So we need to make sure that the value
+    # we return from this function also has a VAIMAcc which corresponds to the
+    # values in `params`.
+    params = DynamicPPL.setacc!!(params, DynamicPPL.ValuesAsInModelAccumulator(false))
     return last(DynamicPPL.evaluate!!(model, params))
 end