These things come to my mind:
- I experienced recent problems with R 3.5 and KNIME on a Mac (R Problems on macOS (high sierra) since R version 3.5). So if you use R version 3.5 you might want to try using R version 3.4.x instead to test it
- Do you use R as a standalone program or do you use the ‘integrated’ R Binaries (Windows only) (cf. Importing R Code in Knime)
- I have seen problems with KNIME on folders that were managed by Microsoft OneDrive because depending on the configuration it might not properly support the special characters that KNIME relies on (namely the hashtag #)
- considering your other post (reload problem with Excel Reader(XLS)) you might want to check if your file system is still healthy if it can handle the load. You could try to install KNIME on a different drive or move the knime-workflow folder to a different drive