We reproduced the issue as you mentioned by rendering your HTML file to XLSX file format. We found tables are not rendered correctly.
HtmlLoadOptions htmlLoadOptions = new HtmlLoadOptions(LoadFormat.Html);
htmlLoadOptions.AutoFitColsAndRows = true;
string html = File.ReadAllText("e:\\test2\\HTMLTAB.txt");
var workbook = new Workbook(new MemoryStream(Encoding.UTF8.GetBytes(html)), htmlLoadOptions);
We have opened the following new ticket(s) in our internal issue tracking system and will deliver their fixes according to the terms mentioned in Free Support Policies.
Issue ID(s): CELLSNET-52630
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