I have my dividends entered but they are not showing in my sum - this happened early on in my prep and corrected itself - now they have disappeared again....

Do they show up on 1040 line 3?  Why do you think they are not being taxed?  

Even though it shows up as income on the first page,if you have capital gains or qualified dividends the tax is not taken from the tax table but is calculated separately from schedule D.  The tax will be calculated on the Qualified Dividends and Capital Gain Tax Worksheet.  It does not get filed with your return.    See this FAQ

https://ttlc.intuit.com/community/forms/help/form-1040-line-11-amount-is-less-than-standard-irs-tax-table/00/25752

In the online version you need to save your return as a pdf file and include all worksheets to see it.

For the Desktop version you can switch to Forms Mode and open the worksheet to see it.  Click Forms in the upper right (upper left for Mac) and look through the list and open the Qualified Dividends and Capital Gain Tax Worksheet.