WebPOptimizer customizes AdditionalToolArguments property whenever an image is being processed. However, the value of that property is shared among concurrent optimizations. Hence, it was being overwritten by concurrent runs, messing with the -resize parameter for the tool.
Instead, the code should generate request (media) specific arguments to be used, and add those to the default arguments + additional tool arguments given in the config files.
WebPOptimizer customizes AdditionalToolArguments property whenever an image is being processed. However, the value of that property is shared among concurrent optimizations. Hence, it was being overwritten by concurrent runs, messing with the -resize parameter for the tool. Instead, the code should generate request (media) specific arguments to be used, and add those to the default arguments + additional tool arguments given in the config files.