Project won't build from Terminal - error is about asset catalog

If I build my project through Xcode, it builds fine. But when I attempt to build from command line using xcodebuild, I get an error:

CompileAssetCatalog /Users/brmerrym/SiliconLabs/bgx/host/ios/Build/Release-iphoneos/BGXCommander.app BGXCommander/Assets.xcassets
    cd /Users/brmerrym/SiliconLabs/bgx/host/iOS/BGXCommander
    export PATH="/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin:/Applications/Xcode.app/Contents/Developer/usr/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/sbin:/opt/X11/bin:/Library/Frameworks/Mono.framework/Versions/Current/Commands"
    /Applications/Xcode.app/Contents/Developer/usr/bin/actool --output-format human-readable-text --notices --warnings --export-dependency-info /Users/brmerrym/SiliconLabs/bgx/host/iOS/BGXCommander/build/BGXCommander.build/Release-iphoneos/BGXCommander.build/assetcatalog_dependencies --output-partial-info-plist /Users/brmerrym/SiliconLabs/bgx/host/iOS/BGXCommander/build/BGXCommander.build/Release-iphoneos/BGXCommander.build/assetcatalog_generated_info.plist --app-icon AppIcon --compress-pngs --enable-on-demand-resources YES --sticker-pack-identifier-prefix com.silabs.BGXCommander.sticker-pack. --target-device iphone --minimum-deployment-target 10.0 --platform iphoneos --product-type com.apple.product-type.application --compile /Users/brmerrym/SiliconLabs/bgx/host/ios/Build/Release-iphoneos/BGXCommander.app /Users/brmerrym/SiliconLabs/bgx/host/iOS/BGXCommander/BGXCommander/Assets.xcassets
BOMStorage BOMStorageNewWithOptionsAndSys(const char *, CFDictionaryRef, BomSys *) can't open: '/Users/brmerrym/SiliconLabs/bgx/host/ios/Build/Release-iphoneos/BGXCommander.app/Assets.car' No such file or directory
CoreUI: Error: unable to create storage file /Users/brmerrym/SiliconLabs/bgx/host/ios/Build/Release-iphoneos/BGXCommander.app/Assets.car error 'No such file or directory'
/ com.apple.actool.errors */
/Users/brmerrym/SiliconLabs/bgx/host/iOS/BGXCommander/BGXCommander/Assets.xcassets: error: ERROR: Each TDDistiller instance can be distilled only one time!
/ com.apple.actool.compilation-results */
/Users/brmerrym/SiliconLabs/bgx/host/ios/Build/Release-iphoneos/BGXCommander.app/AppIcon60x60@2x.png
/Users/brmerrym/SiliconLabs/bgx/host/ios/Build/Release-iphoneos/BGXCommander.app/AppIcon60x60@3x.png
/Users/brmerrym/SiliconLabs/bgx/host/ios/Build/Release-iphoneos/BGXCommander.app/Assets.car
/Users/brmerrym/SiliconLabs/bgx/host/iOS/BGXCommander/build/BGXCommander.build/Release-iphoneos/BGXCommander.build/assetcatalog_generated_info.plist
** BUILD FAILED **
The following build commands failed:
  CompileAssetCatalog /Users/brmerrym/SiliconLabs/bgx/host/ios/Build/Release-iphoneos/BGXCommander.app BGXCommander/Assets.xcassets
(1 failure)

I tried actually adding assets for the App Icons, etc, but it is still failing. Any ideas? Should I just get rid of the asset catalog? I'm not exactly sure what an asset catalog does (some new way of handling icons?)