It's common to experience accuracy issues with UWB systems when obstacles are present between anchors and tags, as UWB signals can be affected by interference. To address this, consider using products that support multipath mitigation or advanced filtering algorithms to enhance accuracy in challenging environments. Additionally, exploring systems with adaptive anchor placements might help optimize signal paths.

Unfortunately, that's generally a limitation of any static system that doesn't use an RTK style correction (look up rtk gps to get the basic idea).  Essentially the speed of light, which UWB modules rely on to determine position, is different in different materials (the dielectric constant), so an obstacle between the transmitter and receiver changes the time delay, which changes the measured position.

Your options there would be to have a fixed tag with a known position near the moving tag, which is guaranteed to have the same obstacles between it and your other anchors, and use the difference between measured and known fixed distances to those anchors, of the fixed tag, to compute a correction to apply to the moving tag.  Or, and I don't necessarily know if this would work in every situation, you could significantly overconstrain the position finding of the tag (have more anchors than necessary), and it may be possible to compute some corrections to each anchor.  Neither of those is likely to be simple or off the shelf though, you may have to find other means.