Maximum length of USB 3.0 Cable
Regarding the USB 3.x cable length, there is no logical length limit, because the protocol is full-duplex, and protocol responses can be deferred. There are some time-outs of ~3 us for link credit responses, so the length could be of the order of ~100+ m per each link segment. 

The actual cable length limitation comes form signal losses in cable materials which cannot be reasonably corrected by "equalization" function built into USB 3.x receivers. The commonly-defined length of 1 m for USB 3.1 Gen2 speed is based on economically affordable dielectric materials (and wire construction) used in mass production of USB cables. You probably can go 10x of that if you use cables made of low-K teflon wrap and silver-coated "Litz wire" and silver-coated shields, but this kind of cable will cost you an arm and leg. 

Regarding link error, there is a requirement from USB3.1 specifications that each USB downstream-facing port must implement "Link Error Count", see section 7.3.3.1  of USB specifications. (See more avaiable "Link Layer Test Specifications")


  The Link Error Count is defined to record the number of events when a
  port transitions from U0 to Recovery to recover an error event. All
  downstream ports shall implement the Link Error Count.
  
  The operation of Link Error count shall adhere to the following rules.
  
   A port in SuperSpeedPlus operation shall implement the Link Error
  Count that counts up to 65,535 error events. The Link Error Count
  shall saturate if it has reached its maximum count value.
  
   The Link Error Count shall be reset to zero in any one of the following
  conditions.
  1. PowerOn Reset, Hot Reset, or Warm Reset
  2. Directed 
  
   The Link Error Count shall be incremented by one each time a port
  transitions from U0 to Recovery to recover an error event.


I believe the access to Error Count is specific to host controller implementation. Most common xHCI specifications define the location of this register at Offset 8 from every PORTSC register, see Section 5.4.10.

The most common method of checking for link errors is to use USB protocol analyzer, but the instrument itself introduces a signal loss, which usually affects the error statistics.