I suspect your SDcard is failing. The current log has already been deleted and recreated.
I would recommend you get an 8GB MicroSD SDHC level 10 card and replace it.
Try to copy what you can from the old card. Only the files in the root directory are needed, but if you can copy the files in the /iotawatt directory, you may be able to save your history log.
Your unit is very old. I have been seeing a few SDcard failures on vintage units > 3 years in service. In Sept 2021 with release 02_06_06, low-write changes were introduced and I expect cards to last much longer. In your case however, there was significant wear for three years and it’s probably causing your trouble.
I’ll be putting out a service bulletin soon recommending that older cards be replaced. If they are replaced before failure, it’s just a few minutes to copy the card and restart.