Tabulator - Changes since 4.7 or 4.8 not backward compatible?

Question

In a product we used version 4.6.3 of Tabulator to both display/filter tables and to export them to Excel. The code was not written by me, but I needed to move to 4.8 to add new filters in a particular section. This works in the section I worked on, but has caused two strange behaviours in other areas which have not been altered. In particular:

1. Exported Excels now have all cells merged
2. A table which has Groups with internal rows, all "closed" by default, now takes almost a minute to export, whereas it completed in less than one second with version 4.6.3 (we are opening all closed groups one by one and then reverting to the original situation when the export is complete). Between two groups, also one calculated row is present (and we export those as well).

My questions are:

1. Is there some way I can specify not to merge cells? Any hint on what regulates that? I wouldn't know what code to attach here, since I don't know what actually causes this behaviour :(
2. Is there some official / best way to export all data in a table, even the rows inside closed groups?

Since I didn't include code, even just hints are welcome ;)

Thank you very much in advance!