It is the compression that can cause issues. Also, once the App is loaded onto Android, zero compression works best because Android does not have to decompress before displaying them. PNG is a good choice because it scales so well and yes it can be saved uncompressed.
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32bit is absolutely fine for small images that require transparency (exception being the launch icon that should not use transparency).
So I think the files causing the issue are not 100% perfect in some way. You could try running them through a batch process, using something like IrfanView.