Fix avatar issue in 1.8 (corrupted file system?)

A few weeks ago the administrator account on my Elgg 1.8.19 site stopped displaying the avatar picture (it shows the grey default). Other users seem unaffected and removing and re-adding it doesn't help.

I have heard this might be somehow related to timezones and elgg's internal file-system, but I am at a total loss how to fix it.

Any tips are greatly appreciated.