Error: One Paket file '' is missing while restoring

Description

I'm getting an unexpected error.

\.paket\Paket.Restore.targets(226,3): error : One Paket file '' is missing while restoring Web.csproj. Please delete
 'paket-files/paket.restore.cached' and call 'paket restore'. [C:\dev\myrepo\src\Web\Web.
csproj]

Repro steps

I'm using paket with an System.Web project (for SDK style csproj)
<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

I used the paket convert-from-nuget command to set paket up.

I'm then trying to do a paket install, interestingly another proj in the solution is also missing a dll from a referenced package. Not sure if this is related.

Expected behavior

Package install works with no errors.

Actual behavior

I get the error Paket.Restore.targets(226,3): error : One Paket file '' is missing while restoring

Known workarounds

It seems to install correctly and a following restore has no errors.

Start with the reported failure at .paket/Paket.Restore.targets line 226, using the SDK-style System.Web project created by paket convert-from-nuget. Reproduce paket install and inspect paket-files/paket.restore.cached, then run paket restore; done means package installation and restore complete without the missing-file error.