Thanks for reaching out and welcome to the forum. So after consulting with the team it seems that you may be using an op that is partially implemented in WASM which is why you do not get an op not supported error - as technically it is supported, but not fully implemented yet so some parameters that are being sent to WebGL version are being thrown away / never used in the WASM version.
It seems your model is composed of the following ops:
Add: 51
AddN: 20
AddV2: 45
Const: 504
Conv2D: 22
Conv2DBackpropInput: 2
DepthwiseConv2dNative: 18
GatherV2: 40
Identity: 21
Maximum: 1
Mean: 82
Merge: 20
Minimum: 1
MirrorPad: 20
Mul: 86
Neg: 20
Pack: 4
Pad: 4
Placeholder: 1
Relu: 14
Rsqrt: 41
Shape: 23
Slice: 22
SquaredDifference: 41
StridedSlice: 14
Sub: 53
Switch: 60

This list was generated using your model.json file and then within tfjs-converter directory executing:
yarn model-summary path_to_model_json_file
My understanding is that one of these ops may be “partial” and this is why error is occuring.
For now if you are unable to change code to not use the offending op, your best bet is to force WebGL to ensure it always uses this for execution assuming WebGL is available (which it should be on most regular laptops/smartphones as 97.9% support on CanIUse 3).
tf.setBackend('webgl');