Underestimate adverbs are provided in this article. The words listed here are commonly found along with the verb underestimate in sentences. This reference page helps answer the question what are some adverbs that describe or modify the verb UNDERESTIMATE.
consistently, greatly
grossly, probably
seriously, significantly
Hope this word list had the underestimate adverb you were looking for. In addition to adverbs used with underestimate, other example verb adverb pairings can be found on this site.
You can help by adding more adverbs in the comments. Thanks.