PWM signal problem

Unfortunately the oscilloscope screenshot has no scaling information, otherwise one could restrict the number of possible explainations. A time expanded view would be also meaningful. But anyway, a FPGA I/O hardly can't source a similar waveform. An oscilloscope probe inadvertently connected to a 50 ohms input may expose it (depending on the selected timebase), also a defective probe. But it's basic electronics, not particularly related to FPGA.