I have been using Pixelfed since late 2020 and basically throughout that time there has been a constant issue with federation reliability. The problem applies to both my own posts (sometimes they do not appear on the official Pixelfed instance, on pixelfed.de, or on mastodon.social) as well as the posts of people I follow (almost every day I can see that some posts from people I follow do not appear on my timeline). This problem also affects comments.