LO Calc hangs saving large xlsx files

I have problems working with LO Calc on large (10-40MB) spreadsheets. The spreadsheets contain large amounts of text (few thousands of news article texts, each in one cell). It takes a very long time to save them, copying large numbers of cells to clipboard causes calc to freeze completely, and I end up having to force quit. Both actions also cause the soffice.bin CPU usage to spike to %100. MEM use also hit 100%, though more gradually. Even navigating between cells can at times cause hangs. I have a fairly modern laptop with an ssd drive and no performance issues otherwise. I used to have the same issue in LO v.5.3.x in the past and upgrading to v.6 seemed to improve the situation somewhat. But it is back to debilitating levels now after a clean OS install with the LO version packed with the distro. I’m sorry if this is a duplicate. I’m aware that similar issues have been brought up in various forums in the past but the ones I’ve seen are closed without a solution. Many thanks in advance for any help. (current LO V. OS:Linux Mint 19)

Does it happen also saving it in .ods format?