.net core webapi causes iis application pool to shutdown - iis

Question

Background:
I'm building a .net core webapi does practically nothing more than checking if a given URL exists and returns the result. If a URL exists and is a redirect (301, 302), the api follows the redirect and returns that result as well. The webapi is called by an SPA which does an api-call for every given url in a checkrequest-queue. So, if someone adds 500 urls to the queue the SPA will loop through it and will send 500 calls to the API – something I could improve upon.
The problem:
My IIS application pool is being shut down on a regular basis due to high CPU usage and/or memory usage:
A worker process serving application pool 'api.domain.com(domain)(4.0)(pool)' has requested a recycle because it reached its private bytes memory limit.
The only way to get my API going again is to manually restart the application. I don't think the operations performed by the API are that demanding, but I surely must be doing something wrong here. Can somebody help me please? The code called by the SPA is:
var checkResponse = new CheckResponse();
var httpMethod = new HttpMethod(request.HttpMethod.ToUpper());
var httpRequestMessage = new HttpRequestMessage(httpMethod, request.Url);
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;
var httpResponseMessage = await httpClient.SendAsync(httpRequestMessage);
checkResponse.RequestMessage = httpResponseMessage.RequestMessage;
checkResponse.Headers = httpResponseMessage.Headers;
checkResponse.StatusCode = httpResponseMessage.StatusCode;
switch (httpResponseMessage.StatusCode)
{
case HttpStatusCode.Ambiguous:
case HttpStatusCode.Found:
case HttpStatusCode.Moved:
case HttpStatusCode.NotModified:
case HttpStatusCode.RedirectMethod:
case HttpStatusCode.TemporaryRedirect:
case HttpStatusCode.UseProxy:
var redirectRequest = new CheckRequest
{
Url = httpResponseMessage.Headers.Location.AbsoluteUri,
HttpMethod = request.HttpMethod,
CustomHeaders = request.CustomHeaders
};
checkResponse.RedirectResponse = await CheckUrl(redirectRequest);
break;
}
The Action on my ApiController:
[HttpPost]
public async Task<IActionResult> Post([FromBody] CheckRequest request)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
var result = await CheckService.CheckUrl(request);
return Ok(result);
}