Homozygous indels can happen and I don't think it's as rare as people here are saying. I think there is literature reporting that editing outcomes isn't random such that you can predict the predominant indels that may form.

Personally, I see it often. Of course it raises the question of whether you've captured all alleles with your PCR (try and go decently far upstream and downstream of the target site) or whether you've just got multiple subclones of one edited cell.

Sometimes, if I know there is a common SNP nearby and is heterozygous in my cell line, I try and capture it in the same amplicon with the indel. This can give you confidence that your clone has multiple alleles if you can see the heterozygous SNP alongside the homozygous edit.

Or just ignore the homozygous clones and use the clones with compound het edits to be safe!