[Desktop] AC split between anon wallet and Uphold wallet does not contribute correctly

[LaurenWags]

Description

If Auto Contribute is split between restored anon wallet/user funds and KYC'd Uphold wallet, the Uphold portion does not complete as expected. Note - AC with only Uphold wallet does work as expected.

Steps to Reproduce

1. Clean profile, staging, short-retries, short reconcile-interval
2. Enable Rewards, don't claim UGP
3. Fund anon card w/ 5 BAT (restore wallet w/ previously anonymously funded 5 BAT)
4. Connect KYC'd uphold acct with at least 5 BAT (note, may need to use Charles Proxy to prevent user funds from moving to Uphold acct)
5. Add sites to AC list (ddg, 3zsistemi, google) - keep default monthly budget of 10 BAT
6. Wait for AC to complete
   --> only anon card BAT is contributed, no BAT from Uphold is contributed

Actual result:

First time I tried this, I got the generic "There has been a problem processing your contribution" error on BAT logo and no BAT was removed from my Uphold acct, so my balance only decreased by 5 BAT.

The second time I tried this, BAT was removed from my Uphold account but seemingly never contributed (UI only reflected 5 BAT in summary instead of the 10 it should have been) - however, by entire wallet balance decreased by 10 BAT.

Expected result:

anon wallet/Uphold split AC should contribute as expected.

Reproduces how often:

easily

Brave version (brave://version info)

Brave	1.10.88 Chromium: 83.0.4103.97 (Official Build) (64-bit)
Revision	326d148b9655369b86498d9ecca39f63dd2bdd2d-refs/branch-heads/4103@{#657}
OS	macOS Version 10.14.6 (Build 18G3020)

Version/Channel Information:

• Can you reproduce this issue with the current release?
• Can you reproduce this issue with the beta channel?
• Can you reproduce this issue with the dev channel?
• Can you reproduce this issue with the nightly channel?

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Miscellaneous Information:

cc @NejcZdovc @rebron @brave/legacy_qa