This is the relevant section in your file, you have to delete the lines with the asterisk at the front:
[Containments][363][Applets][382]
immutability=1
plugin=org.kde.plasma.plasm6desktopindicator
* [Containments][363][Applets][398]
* immutability=1
* plugin=org.kde.plasma.systemmonitor.memory
* [Containments][363][Applets][398][Configuration]
* CurrentPreset=org.kde.plasma.systemmonitor
* PreloadWeight=95
* popupHeight=164
* popupWidth=140
* [Containments][363][Applets][398][Configuration][Appearance]
* chartFace=org.kde.ksysguard.applicationstable
* title=Memory Usage
* [Containments][363][Applets][398][Configuration][ConfigDialog]
* DialogHeight=480
* DialogWidth=640
* [Containments][363][Applets][398][Configuration][SensorColors]
* memory/physical/used=110,89,145
* [Containments][363][Applets][398][Configuration][Sensors]
* highPrioritySensorIds=["memory/physical/used"]
* lowPrioritySensorIds=["memory/physical/total"]
* totalSensors=["memory/physical/usedPercent"]
[Containments][363][Applets][399]
immutability=1
plugin=org.kde.plasma.systemmonitor.net
Then save and close the editor → reboot and pray.