How did you read that data into Matlab? If you look at the CSV using a text editor there are some things to take care about
* In general the data is not sorted by timestamp, you have to do that. That looks like being the cause for the slower ramp being at different positions. I'm not sure if Matlab is capable to process the time stamp written into that files.
* Data is shown in 1 minute intervals for some recent days, looks like that's being the part where your ramps look slower. The remaining data is stored in 10 minute intervals* consumption data is saved as Wh withing the respective time interval. So if the time interval is 10 minutes you will find 10/60 = 1/6 of the consumed power, if the timer interval is 1 minute just 1/60!
* Maybe you number format and /or delimiter is wrong. This Matlab might import the decimal places as seperate column or ignore them
* The data recorded might include text like "undervoltage", "overvoltage" or "N/A" instead of numbers in any column, which also might lead to errors parsing the CSV with the standard functions.
I have done a similar import in GNU Octave (a free "Matlab clone") - not able to deal with all special cases seen in the logfiles so far.
Best regards