I am not sure, the table is similar to the others in the manual. It
could be the "multicolumn" command. It is used to merge the 3 columns
into one and would coincide with the fact that the html version has 2
more empty columns. However, that command is also present in the other
tables and has not given any problems.

Andrei and Georgy, can you figure out what the cause might be?

Another possibility is having rigidly set the size of the columns,
giving an exact number of cm.
Phyllis, try replacing the first row of the tables with the following:

First table:

\begin{longtable}[h] { | p{0.5\textwidth-2\tabcolsep} |
p{0.25\textwidth-2\tabcolsep} | p{0.25\textwidth-2\tabcolsep} | }


Second table:

\begin{longtable}[h] { | p{0.5\textwidth-2\tabcolsep} |
p{0.5\textwidth-2\tabcolsep} | }
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