To reproduce:

• create a dynamic gexf file with dynamic edge attributes.
  
• create a value for one edge attribute, the timestamp of the attribute should be the same for the "end" and "start" period.
  
• importing the gexf then results in a silent fail.
  
• suggested fix: include a report on this error in the import window
  

See this forum thread for the user report:

https://forum.gephi.org/viewtopic.php?f=4&t=2073&start=0