From the log, it appears that there is no binary zip executable or ZipArchive available. When this happens, UpdraftPlus has to use the slowest method for creating zip files. It might be work asking your hosts/server admin to enable the PHP ZipArchive module or a zip executable.
You could also try reducing your archive split. To do this goto the ‘Expert settings’ section of the UpdraftPlus page, and reduce the default setting for how much data is stored in each zip file. e.g. Reduce it from the default of 400Mb down to 100Mb. This will mean that UpdraftPlus spends less time in manipulating large zip files – which can use a lot of resources and be quite time-consuming, especially on slower servers.