Errors when including covariates in metaSEM

I have been attempting to add covariates to a network meta-analytic model that I'm fitting in metaSEM. As a brief bit of background, the network meta-analytic model is designed to model comparisons between a reference group and a set of other groups. Each comparison between the reference and other groups is modeled as a separate outcome. The S matrix in these models is often quite sparse because it is often the case that only ~half the studies contain multi-group designs, so one often needs to place constraints (e.g., with RE.constraints in metaSEM) on the between-studies covariance matrix for the model to be identifiable.

I am able to fit the model with a covariate using the mvmeta package in R, and I have verified that there is variance in my covariate for each of the outcomes (i.e., comparisons between reference and other groups) in the meta-analysis. However, when I attempt to fit the model with the single covariate in metaSEM, I receive the following error:

Error in lm.fit(x, y, offset = offset, singular.ok = singular.ok, ...) :
0 (non-NA) cases

Does anybody have any idea what's happening here? For reference, I have tried fitting the covariate model on subsets of the data (i.e., using only one of the 11 outcomes from the meta-analysis) without generating these errors. My data and a script are attached.