HTTP/1.1 has a limit, set by each individual browser vendor, for the maximum number of connections between a client and a unique server domain. So, if you exceed 6 simultaneous connections to that server (across multiple tabs and windows), it will move the request to a stalled state (like a queue) until one request is completed.

Best solution today is to move to http2 on your server -- which has an SSL (TLS 1.2) requirement.

Looks like pocketbase implements this. If you use another server, like nginx, you have to enable this for each site.