SSRs influenced by physical proximity?
Omeron has a good site/article on this, I had similar problems when trying to design a circuit that could switch from 220V to 110. Adding a snubber with the right values worked for me. Having an oscilloscope and probing the inductive load vs the AC input can tell you whether you have a power factor problem.  

Here are the details, there are two ways the SSR can stay on (on the output):


  Reset Failure due to Solid-state Relay Leakage Current
  
  Reset Failure due to Solid-state Relay Leakage Current Even when there
  is no input signal to the Solid-state Relay there is a small Leakage
  Current (IL) from the Solid-state Relay output (LOAD). If this Leakage
  Current is larger than the load release current, the Solid-state Relay
  may fail to reset. Connect the bleeder resistance R in parallel to
  increase the Solid-state Relay switching current.
  
  \$R&lt;\frac{E}{I_L-I}\$ Where E is the load reset voltage, I is the Load
  reset current, and I_L is the leakage current.




Source: http://www.omron-ap.com/service_support/FAQ/FAQ02155/index.asp

The other problem having an inductive load with a zero crossing SSR, can be a problem if the inductive load is switching 


  Reset Failure Using Load with Low Power Factor
  
  If the power factor of the load is low (guideline: cosΦ=0.4 max.), the
  delay in the load current phase will increase relative to the load
  power supply voltage phase, and a large transient voltage (dv/dt) will
  be applied to the Solid-state Relay when it is about to turn OFF
  (i.e., the load current is near zero), resulting in the possibility of
  the Solid-state Relay not being able to turn OFF (commutation
  failure).
  
  The Solid-state Relay has a built-in CR snubber circuit to limit the
  rate of change in the transient voltage, but leakage current will
  increase if the C value is increased, and reset failure in item 1
  above may occur, so the C value is set to the greatest common factor.
  
  Therefore, if reset failure occurs because the load power factor is
  low, the rate of change in the transient voltage can be limited to
  prevent reset failure by connecting a capacitor and resistor in
  parallel with the Solid-state Relay load terminals.
  
  The capacitor and resistor must be checked to match the load, but
  previous experience shows that a resistor of 100 Ω/1 W and a capacitor
  of 0.1 μF/250 VAC will prevent reset failure.
  
  Also, as mentioned above, the leakage current will increase, so check
  that the reset failure in item 1 does not occur.




Source: http://www.omron-ap.com/service_support/FAQ/FAQ02155/index.asp