diff -Naur a/modules/md/md_curl.c b/modules/md/md_curl.c
--- a/modules/md/md_curl.c	2021-07-12 10:04:51.000000000 +0200
+++ b/modules/md/md_curl.c	2021-09-19 19:14:35.987795057 +0200
@@ -491,7 +491,7 @@
             else if (APR_STATUS_IS_ENOENT(rv)) {
                 md_log_perror(MD_LOG_MARK, MD_LOG_TRACE3, 0, p, 
                               "multi_perform[%d reqs]: no more requests", requests->nelts);
-                if (!running) {
+                if (!requests->nelts) {
                     goto leave;
                 }
                 break;
@@ -524,13 +524,13 @@
         }
 
         /* process status messages, e.g. that a request is done */
-        while (1) {
+        while (running < requests->nelts) {
             curlmsg = curl_multi_info_read(curlm, &msgcount);
             if (!curlmsg) break;
             if (curlmsg->msg == CURLMSG_DONE) {
                 req = find_curl_request(requests, curlmsg->easy_handle);
                 if (req) {
-                    md_log_perror(MD_LOG_MARK, MD_LOG_TRACE3, 0, p, 
+                    md_log_perror(MD_LOG_MARK, MD_LOG_TRACE2, 0, p,
                                   "multi_perform[%d reqs]: req[%d] done", 
                                   requests->nelts, req->id);
                     update_status(req);
@@ -546,7 +546,6 @@
                 }
             }
         }
-        assert(running == requests->nelts);
     };
 
 leave:
diff -Naur a/modules/md/md_ocsp.c b/modules/md/md_ocsp.c
--- a/modules/md/md_ocsp.c	2021-07-12 10:04:51.000000000 +0200
+++ b/modules/md/md_ocsp.c	2021-09-19 19:14:35.987795057 +0200
@@ -339,7 +339,7 @@
     rv = md_cert_get_ocsp_responder_url(&ostat->responder_url, reg->p, cert);
     if (APR_SUCCESS != rv) {
         md_log_perror(MD_LOG_MARK, MD_LOG_ERR, rv, reg->p,
-                      "md[%s]: certificate with serial %s has not OCSP responder URL",
+                      "md[%s]: certificate with serial %s has no OCSP responder URL",
                       name, md_cert_get_serial_number(cert, reg->p));
         goto cleanup;
     }
@@ -609,7 +609,11 @@
     if (NULL == (ocsp_resp = d2i_OCSP_RESPONSE(NULL, (const unsigned char**)&der.data, 
                                                (long)der.len))) {
         rv = APR_EINVAL;
-        md_result_set(update->result, rv, "response body does not parse as OCSP response");
+
+        md_result_set(update->result, rv,
+                      apr_psprintf(req->pool, "req[%d] response body does not parse as "
+                                   "OCSP response, status=%d, body brigade length=%ld",
+                                   resp->req->id, resp->status, (long)der.len));
         md_result_log(update->result, MD_LOG_DEBUG);
         goto cleanup;
     }
@@ -635,7 +639,7 @@
      * to accept it. */
     switch ((n = OCSP_check_nonce(ostat->ocsp_req, basic_resp))) {
         case 1:
-            md_log_perror(MD_LOG_MARK, MD_LOG_DEBUG, 0, req->pool, 
+            md_log_perror(MD_LOG_MARK, MD_LOG_TRACE3, 0, req->pool,
                           "req[%d]: OCSP respoonse nonce does match", req->id);
             break;
         case 0:
@@ -645,7 +649,7 @@
             goto cleanup;
             
         case -1:
-            md_log_perror(MD_LOG_MARK, MD_LOG_TRACE1, 0, req->pool, 
+            md_log_perror(MD_LOG_MARK, MD_LOG_TRACE3, 0, req->pool,
                           "req[%d]: OCSP respoonse did not return the nonce", req->id);
             break;
         default:
@@ -832,6 +836,9 @@
             md_http_set_on_status_cb(req, ostat_on_req_status, update);
             md_http_set_on_response_cb(req, ostat_on_resp, update);
             rv = APR_SUCCESS;
+            md_log_perror(MD_LOG_MARK, MD_LOG_TRACE2, 0, req->pool,
+                          "scheduling OCSP request for %s, %d request in flight",
+                          ostat->md_name, in_flight);
         }
     }
 cleanup:
diff -Naur a/modules/md/md_reg.c b/modules/md/md_reg.c
--- a/modules/md/md_reg.c	2021-05-12 12:14:42.000000000 +0200
+++ b/modules/md/md_reg.c	2021-09-19 19:14:35.988795057 +0200
@@ -549,7 +549,11 @@
         rv = md_pubcert_load(reg->store, group, md->name, spec, &certs, p);
     }
     if (APR_SUCCESS != rv) goto leave;
-            
+    if (certs->nelts == 0) {
+        rv = APR_ENOENT;
+        goto leave;
+    }
+
     pubcert = apr_pcalloc(p, sizeof(*pubcert));
     pubcert->certs = certs;
     cert = APR_ARRAY_IDX(certs, 0, const md_cert_t *);
diff -Naur a/modules/md/md_store_fs.c b/modules/md/md_store_fs.c
--- a/modules/md/md_store_fs.c	2021-07-12 10:04:51.000000000 +0200
+++ b/modules/md/md_store_fs.c	2021-09-19 19:14:35.988795057 +0200
@@ -508,19 +508,21 @@
 
     rv = md_util_is_dir(*pdir, p);
     if (APR_STATUS_IS_ENOENT(rv)) {
-        md_log_perror(MD_LOG_MARK, MD_LOG_DEBUG, rv, p, "not a directory, creating %s", *pdir);
+        md_log_perror(MD_LOG_MARK, MD_LOG_TRACE3, rv, p, "not a directory, creating %s", *pdir);
         rv = apr_dir_make_recursive(*pdir, perms->dir, p);
         if (APR_SUCCESS != rv) goto cleanup;
         dispatch(s_fs, MD_S_FS_EV_CREATED, group, *pdir, APR_DIR, p);
     }
 
     rv = apr_file_perms_set(*pdir, perms->dir);
-    md_log_perror(MD_LOG_MARK, MD_LOG_DEBUG, rv, p, "mk_group_dir %s perm set", *pdir);
+    md_log_perror(MD_LOG_MARK, MD_LOG_TRACE3, rv, p, "mk_group_dir %s perm set", *pdir);
     if (APR_STATUS_IS_ENOTIMPL(rv)) {
         rv = APR_SUCCESS;
     }
 cleanup:
-    md_log_perror(MD_LOG_MARK, MD_LOG_DEBUG, rv, p, "mk_group_dir %d %s", group, name);
+    if (APR_SUCCESS != rv) {
+        md_log_perror(MD_LOG_MARK, MD_LOG_ERR, rv, p, "mk_group_dir %d %s", group, name);
+    }
     return rv;
 }