diff --git a/docs/backend.md b/docs/backend.md
index 846aafb8..58c2ca8b 100644
--- a/docs/backend.md
+++ b/docs/backend.md
@@ -156,8 +156,11 @@ the runner's graph-cut capacity checks.
 
 Runtime capacity checks also leave 512 MiB of currently free device memory for
 backend scratch buffers and pipelines, including with explicit backend assignments.
-They cap stale free-memory reports by the device's total memory minus tracked
-resident allocations and reject reports that exceed the device's total memory.
+They cap free-memory reports by the device's total memory minus tracked
+resident allocations. Vulkan reports exceeding total memory are rejected because
+its heap-budget subtraction can underflow. Other backends use the cap instead of
+treating such reports as zero free memory. Failed checks log the reported free and
+total memory alongside tracked weight and runtime allocations.
 
 Components are considered in `diffusion`, `te`, `vae` order so that repeatedly
 used diffusion weights have priority. Each component's weights use the first
diff --git a/src/conditioning/conditioner.hpp b/src/conditioning/conditioner.hpp
index db5ad319..d9000a32 100644
--- a/src/conditioning/conditioner.hpp
+++ b/src/conditioning/conditioner.hpp
@@ -2219,7 +2219,10 @@ struct LLMEmbedder : public Conditioner {
                                           false,
                                           deepstack_image_embeds,
                                           image_grids);
-        GGML_ASSERT(!hidden_states.empty());
+        if (hidden_states.empty()) {
+            LOG_ERROR("LLM prompt encoding failed");
+            return {};
+        }
         hidden_states = apply_token_weights(std::move(hidden_states), weights);
         GGML_ASSERT(hidden_states.shape()[1] > prompt_template_encode_start_idx);
 
diff --git a/src/model_manager.cpp b/src/model_manager.cpp
index 9a9fe062..930c6f49 100644
--- a/src/model_manager.cpp
+++ b/src/model_manager.cpp
@@ -1613,7 +1613,8 @@ void ModelManager::remove_runtime_owner(uintptr_t owner_id) {
 
 ModelManager::CapacityCheck ModelManager::check_capacity(
     const DeviceMemoryRequest& request,
-    const std::vector<TensorState*>& states) const {
+    const std::vector<TensorState*>& states,
+    bool log_details) const {
     CapacityCheck result;
     if (request.compute_backend == nullptr || sd_backend_is_cpu(request.compute_backend)) {
         return result;
@@ -1631,16 +1632,23 @@ ModelManager::CapacityCheck ModelManager::check_capacity(
         }
         size_t free_bytes = 0, total_bytes = 0;
         ggml_backend_dev_memory(device, &free_bytes, &total_bytes);
+        const size_t weights_resident = compute_backend_resident_bytes(backend);
+        const size_t other_runtime    = other_runtime_resident_bytes(request.owner_id, backend);
+        const size_t resident         = add(weights_resident, add(other_runtime, request.runtime_resident_bytes));
+        if (log_details) {
+            LOG_WARN("model manager memory on %s: reported free %.2f MB / total %.2f MB, tracked weights %.2f MB / other runtime %.2f MB / current runtime %.2f MB",
+                        ggml_backend_name(backend),
+                        free_bytes / (1024.0 * 1024.0), total_bytes / (1024.0 * 1024.0),
+                        weights_resident / (1024.0 * 1024.0), other_runtime / (1024.0 * 1024.0),
+                        request.runtime_resident_bytes / (1024.0 * 1024.0));
+        }
         if (free_bytes == 0 && total_bytes == 0) {
             return SIZE_MAX;
         }
         // Vulkan's heap budget subtraction can underflow when usage exceeds the budget.
-        if (total_bytes > 0 && free_bytes > total_bytes) {
+        if (total_bytes > 0 && free_bytes > total_bytes && sd_backend_is(backend, "Vulkan")) {
             return size_t{0};
         }
-        const size_t resident = add(compute_backend_resident_bytes(backend),
-                                       add(other_runtime_resident_bytes(request.owner_id, backend),
-                                           request.runtime_resident_bytes));
         if (total_bytes > 0) {
             free_bytes = std::min(free_bytes, resident < total_bytes ? total_bytes - resident : 0);
         }
@@ -1786,7 +1794,7 @@ bool ModelManager::ensure_compute_backend_capacity(
         }
     }
 
-    const auto capacity                = check_capacity(request, required_states);
+    const auto capacity                = check_capacity(request, required_states, true);
     const std::string available_device = capacity.available_device_bytes == SIZE_MAX
                                              ? "unknown"
                                              : sd_format("%.2f MB", capacity.available_device_bytes / (1024.0 * 1024.0));
diff --git a/src/model_manager.h b/src/model_manager.h
index 7f8df59c..f3a6e328 100644
--- a/src/model_manager.h
+++ b/src/model_manager.h
@@ -157,7 +157,8 @@ private:
         }
     };
     CapacityCheck check_capacity(const DeviceMemoryRequest& request,
-                                 const std::vector<TensorState*>& states) const;
+                                 const std::vector<TensorState*>& states,
+                                 bool log_details = false) const;
 
     ggml_backend_buffer_type_t params_buffer_type_for(const TensorState& state) const;
     ggml_backend_buffer_type_t split_buffer_type_for(const TensorState& state) const;