The Free-Electron Laser in Hamburg (FLASH) at Deutsches Elektronen-Synchrotron (DESY), Hamburg Germany is a user facility providing ultra-short, femtosecond laser pulses up to the soft X-ray wavelength range. For the precise regulation of the radio frequency (RF) fields within the 60 superconducting cavities, which are organized in 5 RF stations, digital low level RF (LLRF) control systems based on the MTCA.4 standard were implemented in 2013. Until now experiences with failures potentially due to radiation, overheating, and ageing as well as with the general operation of the control systems have been gained. These have a direct impact on the operation and on the performance of FLASH and will allow future improvements. The lessons learned are not only important for FLASH but also in the scope of European X-ray Free-Electron Laser (X-FEL), which will be operated with the same LLRF control system
