How to resolve errors in Resource.designer.cs when building for Android

My Android build has been reporting errors in Resource.designer.cs, an automatically generated file. The errors result from a full-stop (aka period) being in a couple of entries in the .cs file, as per the image below.

If I look in G:\tfs\myapp\myapp\AndroidForForms\AndroidForForms.Android\Resources\Resource.designer.cs
I see:

            // aapt resource value: 0x7f0b008c
            public const int bottomtab_navarea = 2131427468;

            // aapt resource value: 0x7f0b008d
            public const int bottomtab_tabbar = 2131427469;

But if I look in G:\tfs\myapp\myapp\AndroidForForms\AndroidForForms.Android\obj\Debug\81\designtime\Resource.designer.cs
I see the erroneous

            // aapt resource value: 0x7F030180
            public const int bottomtab.navarea = 2130903424;

            // aapt resource value: 0x7F030181
            public const int bottomtab.tabbar = 2130903425;

Any idea what might be causing this, and how I can fix it? (it was happening before I changed my PCLs to .Net Standard 2, and is still happening afterwards)