I have mitek suture anchor in foot (navicular area) placed in after surgery 8 months ago. Could it be causing my bad foot pain? Podiatrist said no.

Bone anchor pain? It is possible that the anchor is the source of the pain but if it is placed well and not backing out it is unlikely that it would be the cause of your pain i would work with your podiatrist to find the source of the pain.
Possible. Is there any swelling or redness at the site of the surgery? There is always a possibility of infection but i would have expected that to show up earlier. Sometimes there can be a non-infectious granulomatous foreign body reaction to the anchor. Has your podiatrist had any x-rays done?
Need more info. A suture anchor is generally buried in bone and does not cause sx unless it comes loose/pulls out. Whether or not you could have a type of rare metal allergy depends on where your foot pain is in relation to the anchor, what type of surgery you had and what you had it for. Do you have additional problems with your foot? Are you wearing foot friendly shoes with good arch and ankle support?
Maybe. The anchor, if placed properly, should be contained within the navicular bone. Therefore, in a sense your podiatrist may be right. The bigger question is your posterior tibial tendon repair holding up? Maybe the pain is from something else associated with the surgery. May need an MRI to reevaluate.