The attached looks fine as .ODS in Calc:

but saved as HTML is somewhat wrecked:
aaa and bbb rowspan=n has failed to take account of the autofilter. If only one know what value to correct it to:
The attached looks fine as .ODS in Calc:

but saved as HTML is somewhat wrecked:
aaa and bbb rowspan=n has failed to take account of the autofilter. If only one know what value to correct it to: