Layers that are defined with the same start/end date and paired with any number of single year layers (but different year from the other layer) only shows the last layer turned on.
Example:
https://staging.earthtime.org/explore#v=39.31025,-97.50877,3.226,latLng&t=0.04&ps=50&l=state_borders_gray,violence_hate_group_counts_by_state,bdrk,tuft_misinformation_vulnerability_index&bt=20200101&et=20201231&startDwell=0&endDwell=0
vs
https://staging.earthtime.org/explore#v=39.31025,-97.50877,3.226,latLng&t=0.04&ps=50&l=state_borders_gray,tuft_misinformation_vulnerability_index,violence_hate_group_counts_by_state,bdrk&bt=20200101&et=20201231&startDwell=0&endDwell=0