I'm having the same issue related this question: table rowspan page break
In my Visualforce page, my html table has a column with a custom rowspan (depending on the amount of rowspanned rows) and I'm having a style issue (please see the issue in the green square): enter image description here
I'm using a tr with style as page-break-before: auto and a dynamic rowspan (depending on business logic)
I tried with the apge-break-inside in the rowspanned tr, but without result.
I solved my issue by adding inner tables in the rows inside the main table instead of using rowspan property in the 'tr' and not using page breaks:
<table class="general">
<thead style="display: table-header-group; valign: top">
.
.
.
</thead>
<tbody>
<apex:repeat value="{!VALUE}" var="VAR">
<tr>
<td>
<apex:outputText escape="false" value="{!VALUE}" />
</td>
<td>
<table>
<apex:repeat value="{!VALUE}" var="VAR">
<tr>
<td>
<apex:outputText escape="false" value="{!value}" />
</td>
</tr>
</apex:repeat>
</table>
</tr>
</tbody>