Created attachment 196021 [details] the document with the rendering issue The first vertically merged cells in the attached document is not rendered as the following ones, only one cell is rendered at the top. The content of the cells and rows for other vertically merged cells seems the same and are rendered as expected.
Created attachment 196022 [details] The actual rendering
Created attachment 196023 [details] The expected rendering
Opening the file with Microsoft® Word para Microsoft 365 MSO (versión 2407 compilación 16.0.17830.20056) de 64 bits and resaving it with Word, allows opening fine with LibreOffice. Version: 24.8.0.3 (X86_64) / LibreOffice Community Build ID: 0bdf1299c94fe897b119f97f3c613e9dca6be583 CPU threads: 16; OS: Windows 11 X86_64 (10.0 build 22631); UI render: Skia/Raster; VCL: win Locale: es-ES (es_ES); UI: en-US Calc: CL threaded
OK I'll try to do the same and see what differences are in the saved document. So this bug might be invalid.